Classic-quantum injection interface device

ABSTRACT

Novel and useful quantum structures having a continuous well with control gates that control a local depletion region to form quantum dots. Local depleted well tunneling is used to control quantum operations to implement quantum computing circuits. Qubits are realized by modulating gate potential to control tunneling through local depleted region between two or more sections of the well. Complex structures with a higher number of qdots per continuous well and a larger number of wells are fabricated. Both planar and 3D FinFET semiconductor processes are used to build well to gate and well to well tunneling quantum structures. Combining a number of elementary quantum structure, a quantum computing machine is realized. An interface device provides an interface between classic circuitry and quantum circuitry by permitting tunneling of a single quantum particle from the classic side to the quantum side of the device. Detection interface devices detect the presence or absence of a particle destructively or nondestructively.

REFERENCE TO PRIORITY APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/687,800, filed Jun. 20, 2018, entitled “Electric Signal Pulse-WidthAnd Amplitude Controlled And Re-Programmable Semiconductor QuantumRotation Gates,” U.S. Provisional Application No. 62/687,803, filed Jun.21, 2018, entitled “Semiconductor Quantum Structures and ComputingCircuits Using Local Depleted Well Tunneling,” U.S. ProvisionalApplication No. 62/689,100, filed Jun. 23, 2018, entitled “SemiconductorControlled Entangled-Aperture-Logic Quantum Shift Register,” U.S.Provisional Application No. 62/694,022, filed Jul. 5, 2018, entitled“Double-V Semiconductor Entangled-Aperture-Logic Parallel QuantumInteraction Path,” U.S. Provisional Application No. 62/687,779, filedJun. 20, 2018, entitled “Semiconductor Quantum Structures And GatesUsing Through-Thin-Oxide Well-To-Gate Aperture Tunneling,” U.S.Provisional Application No. 62/687,793, filed Jun. 20, 2018, entitled“Controlled Semiconductor Quantum Structures And Computing CircuitsUsing Aperture Well-To-Gate Tunneling,” U.S. Provisional Application No.62/688,341, filed Jun. 21, 2018, entitled “3D Semiconductor QuantumStructures And Computing Circuits Using Fin-To-Gate Tunneling,” U.S.Provisional Application No. 62/689,035, filed Jun. 22, 2018, entitled“3D Semiconductor Quantum Structures And Computing Circuits UsingControlled Tunneling Through Local Fin Depletion Regions,” U.S.Provisional Application No. 62/689,291, filed Jun. 25, 2018, entitled“Semiconductor Quantum Dot And Qubit Structures Using Aperture-TunnelingThrough Oxide Layer,” U.S. Provisional Application No. 62/689,166, filedJun. 24, 2018, entitled “Semiconductor Entangled-Aperture-Logic QuantumAncillary Gates,” U.S. Provisional Application No. 62/692,745, filedJun. 20, 2018, entitled “Re-Programmable And Re-Configurable QuantumProcessor Using Pulse-Width Based Rotation Selection And Path Access OrBifurcation Control,” U.S. Provisional Application No. 62/692,804, filedJul. 1, 2018, entitled “Quantum Processor With Dual-Path Quantum ErrorCorrection,” U.S. Provisional Application No. 62/692,844, filed Jul. 1,2018, entitled “Quantum Computing Machine With Partial Data Readout AndRe-Injection Into The Quantum State,” U.S. Provisional Application No.62/726,290, filed Jun. 20, 2018, entitled “Controlled-NOT and TofolliSemiconductor Entangled-Aperture-Logic Quantum Gates,” U.S. ProvisionalApplication No. 62/695,842, filed Jul. 10, 2018, entitled “EntangledAperture-Logic Semiconductor Quantum Computing Structure withIntermediary Interactor Path,” U.S. Provisional Application No.62/698,278, filed Jul. 15, 2018, entitled “Entangled Aperture-LogicSemiconductor Quantum Bifurcation and Merging Gate,” U.S. ProvisionalApplication No. 62/726,397, filed Sep. 3, 2018, entitled “SemiconductorQuantum Structure With Simultaneous Shift Into Entangled State,” U.S.Provisional Application No. 62/791,818, filed Jan. 13, 2019, entitled“Semiconductor Process for Quantum Structures with Staircase ActiveWell,” U.S. Provisional Application No. 62/788,865, filed Jan. 6, 2018,entitled “Semiconductor Process For Quantum Structures Without InnerContacts And Doping Layers,” U.S. Provisional Application No.62/794,591, filed Jan. 19, 2019, entitled “Semiconductor QuantumStructures Using Localized Aperture Channel Tunneling Through ControlledDepletion Region,” U.S. Provisional Application No. 62/703,888, filedJul. 27, 2018, entitled “Aperture Tunneling Semiconductor Quantum Dotsand Chord-Line Quantum Computing Structures,” U.S. ProvisionalApplication No. 62/726,271, filed Sep. 2, 2018, entitled “ControlledLocal Thermal Activation Of Freeze-Out Semiconductor Circuits ForCryogenic Operation,” U.S. Provisional Application No. 62/731,810, filedSep. 14, 2018, entitled “Multi-Stage Semiconductor Quantum Detector withAnti-Correlation Merged With Quantum Core,” and U.S. ProvisionalApplication No. 62/794,655, filed Jan. 20, 2019, entitled “SemiconductorQuantum Structures Using Preferential Tunneling Direction Through ThinInsulator Layers.” All of which are incorporated herein by reference intheir entirety.

FIELD OF THE DISCLOSURE

The subject matter disclosed herein relates to the field of quantumcomputing and more particularly relates to planar quantum structuresusing tunneling through an oxide layer, tunneling through a localdepleted well, and 3D quantum structures using tunneling through anoxide layer, tunneling through a local depleted fin.

BACKGROUND OF THE INVENTION

Quantum computers are machines that perform computations using thequantum effects between elementary particles, e.g., electrons, holes,ions, photons, atoms, molecules, etc. Quantum computing utilizesquantum-mechanical phenomena such as superposition and entanglement toperform computation. Quantum computing is fundamentally linked to thesuperposition and entanglement effects and the processing of theresulting entanglement states. A quantum computer is used to performsuch computations which can be implemented theoretically or physically.

Currently, analog and digital are the two main approaches to physicallyimplementing a quantum computer. Analog approaches are further dividedinto quantum simulation, quantum annealing, and adiabatic quantumcomputation. Digital quantum computers use quantum logic gates to docomputation. Both approaches use quantum bits referred to as qubits.

Qubits are fundamental to quantum computing and are somewhat analogousto bits in a classical computer. Qubits can be in a |0> or |1> quantumstate but they can also be in a superposition of the |0> and |1> states.When qubits are measured, however, they always yield a |0> or a |1>based on the quantum state they were in.

The key challenge of quantum computing is isolating such microscopicparticles, loading them with the desired information, letting theminteract and then preserving the result of their quantum interaction.This requires relatively good isolation from the outside world and alarge suppression of the noise generated by the particle itself.Therefore, quantum structures and computers operate at very lowtemperatures (e.g., cryogenic), close to the absolute zero kelvin (K),in order to reduce the thermal energy/movement of the particles to wellbelow the energy/movement coming from their desired interaction. Currentphysical quantum computers, however, are very noisy and quantum errorcorrection is commonly applied to compensate for the noise.

Most existing quantum computers use superconducting structures torealize quantum interactions. Their main drawbacks, however, are thefact that superconducting structures are very large and costly and havedifficulty in scaling to quantum processor sizes of thousands ormillions of quantum-bits (qubits). Furthermore, they need to operate atfew tens of milli-kelvin (mK) temperatures, that are difficult toachieve and where it is difficult to dissipate significant power tooperate the quantum machine.

SUMMARY OF THE INVENTION

The present invention discloses several semiconductor based planarquantum structures using tunneling through an oxide layer, tunnelingthrough a local depleted well, and 3D quantum structures using tunnelingthrough an oxide layer, tunneling through a local depleted fin. Thesestructures are used to construct quantum dots (qdots) and quantum bits(qubits) which are in turn used to implement quantum processor andcomputing circuits. Qdots, qubits, quantum gates and structures utilizesemiconductor processes based on tunneling through a local depletedwell. Using a continuous well with overlapping control gates allows thepropagation of a quantum particle in a controlled manner from onesection of the well to another. The barrier generated by the controlgate either locks the particle in a certain region or allows theparticle's wavefunction to partially or completely transition to anothersection of the well.

Interaction and entanglement between two or more particles are realizedin a single continuous well or in structures consisting of a pluralityof continuous wells. Multiple implementation examples adapted for avariety of semiconductor processes are disclosed and described. It isappreciated that similar principles can be applied to other processessuch as nanotubes and 3D processing. Further, the quantum structureprinciple described herein can be applied to a variety of hybridprocesses and components, including semiconductor,microelectromechanical systems (MEMS), passives, integrated passivedevices (IPDs), acoustic, optical, etc.

An interface device provides an interface between classic circuitry andquantum circuitry by permitting tunneling of a single quantum particlefrom the classic side to the quantum side of the device. Detectioninterface devices detect the presence or absence of a particledestructively or nondestructively.

This, additional, and/or other aspects and/or advantages of theembodiments of the present invention are set forth in the detaileddescription which follows; possibly inferable from the detaileddescription; and/or learnable by practice of the embodiments of thepresent invention.

There is thus provided in accordance with the invention, an interfacedevice for interfacing between classic field effect transistor (FET)circuitry and quantum circuitry, comprising a substrate, a firstsubstantially undoped or low-doped well constructed on said substrate inwhich both a classic well and a quantum well are realized, a first dopeddiffusion in or above said first well forming a classic wellconstituting a classic side of said device, a control gate constructedover at least a portion of said first well wherein a potential appliedto said control gate is operative to control a tunneling paththereunder, and a second well formed by a remainder of said first wellon an opposite side of said control gate forming a quantum wellconstituting a quantum side of said device.

There is also provided in accordance with the invention, an interfacedevice for interfacing between classic field effect transistor (FET)circuitry and quantum circuitry, comprising a substrate, a first wellconstructed on said substrate and substantially doped in accordance witha classic FET device to form a classic side, a contact layer operativeto establish an electric connection between a metal layer going to otherclassic devices and said first well, a second well constructed on saidsubstrate and substantially undoped in accordance with a quantumstructure to form a quantum side, a control gate fabricated to overlapat least a portion of said second well, and wherein application of anappropriate potential to said control gate enables tunneling of a singlequantum particle through a local depleted tunneling path between saidfirst well and said second well.

There is further provided in accordance with the invention, an interfacedevice for interfacing between classic field effect transistor (FET)circuitry and quantum circuitry, comprising a substrate, a classic FETwell constructed on said substrate and operative to be connected toclassic FET circuitry to form a classic side, a quantum dot wellconstructed on said substrate and operative to interface with quantumcircuitry to form a quantum side, a control gate constructed over atleast a portion of said quantum dot well, wherein a first pulse signalat a first time instance applied to said control gate controls tunnelingof a single quantum particle through a local depleted tunnel path fromsaid classic side to said quantum side in an injector mode of operation,and wherein a second pulse signal at a second time instance applied tosaid control gate allows tunneling of a single quantum particle througha local depleted tunneling path from the said quantum side to saidclassic side in a detector mode of operation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in further detail in the followingexemplary embodiments and with reference to the figures, where identicalor similar elements may be partly indicated by the same or similarreference numerals, and the features of various exemplary embodimentsbeing combinable. The invention is herein described, by way of exampleonly, with reference to the accompanying drawings, wherein:

FIG. 1 is a high level block diagram illustrating an example quantumcomputer system constructed in accordance with the present invention;

FIG. 2 is a high level block diagram illustrating a quantum structureand its interface using integrated electronic control circuitry;

FIG. 3A is a diagram illustrating a quantum structure beforeinitialization;

FIG. 3B is a diagram illustrating an example ideal and decoherence Rabioscillation waveform;

FIG. 3C is a diagram illustrating a quantum structure initialized to afirst base state;

FIG. 3D is a diagram illustrating an example Rabi oscillation waveformat initialization;

FIG. 3E is a diagram illustrating a quantum structure initialized to asecond base state;

FIG. 3F is a diagram illustrating an example waveform having half theRabi oscillation period;

FIG. 3G is a diagram illustrating a quantum structure with a particle intwo qdots at the same time;

FIG. 3H is a diagram illustrating an example waveform having one quarterthe Rabi oscillation period;

FIG. 3I is a diagram illustrating a first quantum structure with aparticle split between two qdots at the same time;

FIG. 3J is a diagram illustrating an example waveform having a periodless than one quarter the Rabi oscillation period;

FIG. 3K is a diagram illustrating a second quantum structure with aparticle split between two qdots at the same time;

FIG. 3L is a diagram illustrating an example waveform having a periodmore than one quarter the Rabi oscillation period;

FIG. 4A is a diagram illustrating a circular shaped quantum structureincorporating local depleted well tunneling;

FIG. 4B is a diagram illustrating the change in the aperture tunnelbarrier from a wide depletion region to a narrow depletion region;

FIG. 4C is a diagram illustrating a first rectangular shaped quantumstructure incorporating local depleted well tunneling;

FIG. 4D is a diagram illustrating the change in the aperture tunnelbarrier from a wide depletion region to a narrow depletion region;

FIG. 5 is a diagram illustrating a second rectangular shaped quantumstructure incorporating local depleted well tunneling;

FIG. 6 is a diagram illustrating a cross section of an example quantumstructure;

FIG. 7A is a diagram illustrating an example circular shape for thequantum structure of the present invention;

FIG. 7B is a diagram illustrating an example square shape for thequantum structure of the present invention;

FIG. 7C is a diagram illustrating an example square shape with roundedcorners for the quantum structure of the present invention;

FIG. 7D is a diagram illustrating an example hexagonal shape for thequantum structure of the present invention;

FIG. 7E is a diagram illustrating an example rectangular shape for thequantum structure of the present invention;

FIG. 7F is a diagram illustrating an example trapezoidal shape for thequantum structure of the present invention;

FIG. 7G is a diagram illustrating a first example overlapping squareshape for the quantum structure of the present invention;

FIG. 7H is a diagram illustrating a first example ‘L’ shape for thequantum structure of the present invention;

FIG. 7I is a diagram illustrating an example ‘Z’ shape for the quantumstructure of the present invention;

FIG. 7J is a diagram illustrating a second example ‘L’ shape for thequantum structure of the present invention;

FIG. 7K is a diagram illustrating an example barely touching squareshape for the quantum structure of the present invention;

FIG. 7L is a diagram illustrating an example barely touching squareshape with optical proximity control for the quantum structure of thepresent invention;

FIG. 7M is a diagram illustrating an example double square with narrowneck shape for the quantum structure of the present invention;

FIG. 7N is a diagram illustrating a second example overlapping squareshape for the quantum structure of the present invention;

FIG. 7O is a diagram illustrating a third example overlapping squareshape for the quantum structure of the present invention;

FIG. 7P is a diagram illustrating an example barely touching rectangularshape for the quantum structure of the present invention;

FIG. 7Q is a diagram illustrating an example barely touching doubleoverlapping square shape for the quantum structure of the presentinvention;

FIG. 7R is a diagram illustrating an example double square connected viasingle smaller square shape for the quantum structure of the presentinvention;

FIG. 7S is a diagram illustrating an example double square connected viadouble smaller square shape for the quantum structure of the presentinvention;

FIG. 8A is a diagram illustrating a first example control gate for thequantum structure of the present invention;

FIG. 8B is a diagram illustrating a second example control gate for thequantum structure of the present invention;

FIG. 8C is a diagram illustrating a third example control gate for thequantum structure of the present invention;

FIG. 9A is a diagram illustrating an example quantum structure withdouble square shape;

FIG. 9B is a diagram illustrating an example quantum structure withdouble square shape and optical proximity control;

FIG. 9C is a diagram illustrating an example quantum structure withdouble square and narrow neck shape;

FIG. 9D is a diagram illustrating a first example quantum structure withdouble overlapping square shape;

FIG. 9E is a diagram illustrating a second example quantum structurewith double overlapping square shape;

FIG. 9F is a diagram illustrating an example quantum structure with ‘L’shape;

FIG. 9G is a diagram illustrating an example quantum structure withdouble rounded barely touching square shape;

FIG. 9H is a diagram illustrating an example quantum structure withdouble rectangular shape;

FIG. 9I is a diagram illustrating an example quantum structure withdouble square connected via double smaller square shape;

FIG. 9J is a diagram illustrating an example quantum structure withdouble rounded square with narrow neck shape;

FIG. 9K is a diagram illustrating an example quantum structure with anoverlapping pair of double rounded squares with narrow neck shape;

FIG. 9L is a diagram illustrating a first example quantum structure witha pair of barely touching double overlapping square shape;

FIG. 9M is a diagram illustrating a second example quantum structurewith a pair of barely touching double overlapping square shape;

FIG. 9N is a diagram illustrating a first example quantum structure witha double square shape with narrow neck and butterfly shaped controlgate;

FIG. 9O is a diagram illustrating a second example quantum structurewith a double square shape with narrow neck and butterfly shaped controlgate;

FIG. 9P is a diagram illustrating an example quantum structure with apair of overlapping double square shapes with narrow neck and butterflyshaped control gates;

FIG. 9Q is a diagram illustrating an example conventional FET with drainand source doped diffusion and contacts;

FIG. 9R is a diagram illustrating an example half conventional FET andhalf quantum structure;

FIG. 9S is a diagram illustrating an example quantum structure withrectangular shaped wells;

FIG. 9T is a diagram illustrating an example quantum structure withdissimilar rectangular shaped wells;

FIG. 9U is a diagram illustrating an example quantum structure withoffset rectangular shaped wells;

FIG. 9V is a diagram illustrating a first example quantum structure withspaced apart rectangular shaped wells;

FIG. 9W is a diagram illustrating a first example quantum structure withspaced apart rectangular shaped wells offset from each other;

FIG. 9X is a diagram illustrating a second example quantum structurewith spaced apart rectangular shaped wells;

FIG. 9Y is a diagram illustrating a second example quantum structurewith spaced apart rectangular shaped wells offset from each other;

FIG. 9Z is a diagram illustrating a third example quantum structure withspaced apart rectangular shaped wells offset from each other;

FIG. 9AA is a diagram illustrating a fourth example quantum structurewith spaced apart rectangular shaped wells offset from each other;

FIG. 9AB is a diagram illustrating a first example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AC is a diagram illustrating a second example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AD is a diagram illustrating a third example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AE is a diagram illustrating a fourth example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AF is a diagram illustrating a fifth example quantum structurewith corner abutting rectangular shaped wells;

FIG. 9AG is a diagram illustrating a sixth example quantum structurewith corner abutting rectangular shaped wells;

FIG. 10A is a diagram illustrating a first example interface device ofthe present invention in more detail;

FIG. 10B is a diagram illustrating a second example interface device ofthe present invention;

FIG. 10C is a diagram illustrating a third example interface device ofthe present invention;

FIG. 11 is a diagram illustrating a cross section of a first examplequantum structure and conventional FET;

FIG. 12 is a diagram illustrating a cross section of a second examplequantum structure and conventional FET;

FIG. 13 is a diagram illustrating a cross section of a third examplequantum structure and conventional FET;

FIG. 14 is a diagram illustrating an example quantum structure withinterface devices;

FIG. 15A is a diagram illustrating a first example multiple qdot quantumstructure with interface devices on either end thereof;

FIG. 15B is a diagram illustrating an example layout of an examplequantum structure;

FIG. 16 is a diagram illustrating a cross section of the quantumstructure of FIG. 15A;

FIG. 17A is a diagram illustrating the aperture tunnel barrier for a twoquantum dot structure;

FIG. 17B is a diagram illustrating a first example change in theaperture tunnel barrier for the two quantum dot structure;

FIG. 17C is a diagram illustrating a second example change in theaperture tunnel barrier for the two quantum dot structure;

FIG. 18 is a diagram illustrating an example quantum structuresurrounded by a spin control magnetic coil;

FIG. 19 is a diagram illustrating a second example multiple qdot quantumstructure;

FIG. 20 is a diagram illustrating a third example multiple qdot quantumstructure;

FIG. 21 is a diagram illustrating a fourth example multiple qdot quantumstructure;

FIG. 22A is a diagram illustrating an example floating well detectioncircuit;

FIG. 22B is a diagram illustrating the layout for the example floatingwell detection circuit;

FIG. 22C is a diagram illustrating the cross section for the floatingwell detection circuit;

FIG. 23A is a diagram illustrating an example floating gate detectioncircuit;

FIG. 23B is a diagram illustrating the layout for the example floatinggate detection circuit;

FIG. 23C is a diagram illustrating the cross section for the floatinggate detection circuit;

FIG. 24 is an example potential diagram for the floating gate detectioncircuit;

FIG. 25 is a diagram illustrating an example 3D semiconductor quantumstructure using fin to fin tunneling through local depletion region;

FIG. 26 is a diagram illustrating a three dimensional view of an example3D semiconductor quantum structure with fin to fin tunneling undercontrol of a control gate;

FIG. 27A is a diagram illustrating a cross section, side view, and topview of an example 3D two qdot quantum structure using local findepletion tunneling;

FIG. 27B is a diagram illustrating a cross section, side views, and topview of an example 3D multiple qdot quantum structure using local findepletion tunneling;

FIG. 28A is a diagram illustrating two example double V fin-gate-finstructures having two wells placed in close proximity allowing quantumparticles to interact;

FIG. 28B is a diagram illustrating an example 3D semiconductor quantumstructure using fin-to-fin tunneling through a local depleted regionwith a shared well between two fin paths providing bifurcation;

FIG. 28C is a diagram illustrating an example quantum structure withdummy gates and gate cuts that separate control and dummy gates;

FIG. 28D is a diagram illustrating an example hybrid planar and 3Dsemiconductor quantum structure using both fin-to-fin and well-to-welltunneling through local depletion region;

FIG. 29 is a diagram illustrating an example 3D semiconductor quantumstructure using fin-to-gate tunneling through oxide;

FIG. 30 is a diagram illustrating a three dimensional view of an example3D semiconductor quantum structure using fin-to-gate and gate-to-fintunneling through oxide;

FIG. 31 is a diagram illustrating a cross section, side view, and topview of an example 3D semiconductor quantum structure using fin-to-gatetunneling through oxide;

FIG. 32 is a diagram illustrating a cross section of an example 3Dsemiconductor quantum structure using fin-to-gate and gate-to-fintunneling;

FIG. 33 is a diagram illustrating a top view of an example two qdot 3Dsemiconductor quantum structure using fin-to-gate tunneling throughoxide;

FIG. 34A is a diagram illustrating an example double V quantuminteraction structure using 3D semiconductor process with fin-to-gatetunneling;

FIG. 34B is a diagram illustrating an example quantum structure withfin-to-gate tunneling with dummy gates and cuts to create dummy fins;and

FIG. 34C is a diagram illustrating an example hybrid planar and 3Dsemiconductor quantum structure using both fin-to-gate and well-to-gatetunneling.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention. Itwill be understood by those skilled in the art, however, that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Among those benefits and improvements that have been disclosed, otherobjects and advantages of this invention will become apparent from thefollowing description taken in conjunction with the accompanyingfigures. Detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the invention that may be embodied in variousforms. In addition, each of the examples given in connection with thevarious embodiments of the invention which are intended to beillustrative, and not restrictive.

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings.

The figures constitute a part of this specification and includeillustrative embodiments of the present invention and illustrate variousobjects and features thereof. Further, the figures are not necessarilyto scale, some features may be exaggerated to show details of particularcomponents. In addition, any measurements, specifications and the likeshown in the figures are intended to be illustrative, and notrestrictive. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention. Further, where considered appropriate,reference numerals may be repeated among the figures to indicatecorresponding or analogous elements.

Because the illustrated embodiments of the present invention may for themost part, be implemented using electronic components and circuits knownto those skilled in the art, details will not be explained in anygreater extent than that considered necessary, for the understanding andappreciation of the underlying concepts of the present invention and inorder not to obfuscate or distract from the teachings of the presentinvention.

Any reference in the specification to a method should be applied mutatismutandis to a system capable of executing the method. Any reference inthe specification to a system should be applied mutatis mutandis to amethod that may be executed by the system.

Throughout the specification and claims, the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise. The phrases “in one embodiment,” “in an exampleembodiment,” and “in some embodiments” as used herein do not necessarilyrefer to the same embodiment(s), though it may. Furthermore, the phrases“in another embodiment,” “in an alternative embodiment,” and “in someother embodiments” as used herein do not necessarily refer to adifferent embodiment, although it may. Thus, as described below, variousembodiments of the invention may be readily combined, without departingfrom the scope or spirit of the invention.

In addition, as used herein, the term “or” is an inclusive “or”operator, and is equivalent to the term “and/or,” unless the contextclearly dictates otherwise. The term “based on” is not exclusive andallows for being based on additional factors not described, unless thecontext clearly dictates otherwise. In addition, throughout thespecification, the meaning of “a,” “an,” and “the” include pluralreferences. The meaning of “in” includes “in” and “on.”

The following definitions apply throughout this document.

A quantum particle is defined as any atomic or subatomic particlesuitable for use in achieving the controllable quantum effect. Examplesinclude electrons, holes, ions, photons, atoms, molecules, artificialatoms. A carrier is defined as an electron or a hole in the case ofsemiconductor electrostatic qubit. Note that a particle may be split andpresent in multiple quantum dots. Thus, a reference to a particle alsoincludes split particles.

In quantum computing, the qubit is the basic unit of quantuminformation, i.e. the quantum version of the classical binary bitphysically realized with a two-state device. A qubit is a two statequantum mechanical system in which the states can be in a superposition.Examples include (1) the spin of the particle (e.g., electron, hole) inwhich the two levels can be taken as spin up and spin down; (2) thepolarization of a single photon in which the two states can be taken tobe the vertical polarization and the horizontal polarization; and (3)the position of the particle (e.g., electron) in a structure of twoqdots, in which the two states correspond to the particle being in oneqdot or the other. In a classical system, a bit is in either one stateor the other. Quantum mechanics, however, allows the qubit to be in acoherent superposition of both states simultaneously, a propertyfundamental to quantum mechanics and quantum computing. Multiple qubitscan be further entangled with each other.

A quantum dot or qdot (also referred to in literature as QD) is ananometer-scale structure where the addition or removal of a particlechanges its properties is some ways. In one embodiment, quantum dots areconstructed in silicon semiconductor material having typical dimensionin nanometers. The position of a particle in a qdot can attain severalstates. Qdots are used to form qubits and qudits where multiple qubitsor qudits are used as a basis to implement quantum processors andcomputers.

A quantum interaction gate is defined as a basic quantum logic circuitoperating on a small number of qubits or qudits. They are the buildingblocks of quantum circuits, just like the classical logic gates are forconventional digital circuits.

A qubit or quantum bit is defined as a two state (two level) quantumstructure and is the basic unit of quantum information. A qudit isdefined as a d-state (d-level) quantum structure. A qubyte is acollection of eight qubits.

The terms control gate and control terminal are intended to refer to thesemiconductor structure fabricated over a continuous well with a localdepleted region and which divides the well into two or more qdots. Theseterms are not to be confused with quantum gates or classical FET gates.

Unlike most classical logic gates, quantum logic gates are reversible.It is possible, however, although cumbersome in practice, to performclassical computing using only reversible gates. For example, thereversible Toffoli gate can implement all Boolean functions, often atthe cost of having to use ancillary bits. The Toffoli gate has a directquantum equivalent, demonstrating that quantum circuits can perform alloperations performed by classical circuits.

A quantum well is defined as a low doped or undoped continuous depletedsemiconductor well that functions to contain quantum particles in aqubit or qudit. The quantum well may or may not have contacts and metalon top. A quantum well holds one free carrier at a time or at most a fewcarriers that can exhibit single carrier behavior.

A classic well is a medium or high doped semiconductor well contactedwith metal layers to other devices and usually has a large number offree carriers that behave in a collective way, sometimes denoted as a“sea of electrons.”

A quantum structure or circuit is a plurality of quantum interactiongates. A quantum computing core is a plurality of quantum structures. Aquantum computer is a circuit having one or more computing cores. Aquantum fabric is a collection of quantum structures, circuits, orinteraction gates arranged in a grid like matrix where any desiredsignal path can be configured by appropriate configuration of accesscontrol gates placed in access paths between qdots and structures thatmake up the fabric.

In one embodiment, qdots are fabricated in low doped or undopedcontinuous depleted semiconductor wells. Note that the term ‘continuous’as used herein is intended to mean a single fabricated well (even thoughthere could be structures on top of them, such as gates, that modulatethe local well's behavior) as well as a plurality of abutting contiguouswells fabricated separately or together, and in some cases mightapparently look as somewhat discontinuous when ‘drawn’ using a computeraided design (CAD) layout tool.

The term classic or conventional circuitry (as opposed to quantumstructures or circuits) is intended to denote conventional semiconductorcircuitry used to fabricate transistors (e.g., FET, CMOS, BIT, FinFET,etc.) and integrated circuits using processes well-known in the art.

The term Rabi oscillation is intended to denote the cyclic behavior of aquantum system either with or without the presence of an oscillatorydriving field. The cyclic behavior of a quantum system without thepresence of an oscillatory driving field is also referred to asoccupancy oscillation.

Throughout this document, a representation of the state of the quantumsystem in spherical coordinates includes two angles θ and φ. Consideringa unitary sphere, as the Hilbert space is a unitary state, the state ofthe system is completely described by the vector Ψ. The vector Ψ inspherical coordinates can be described in two angles θ and φ. The angleθ is between the vector Ψ and the z-axis and the angle φ is the anglebetween the projection of the vector on the XY plane and the x-axis.Thus, any position on the sphere is described by these two angles θ andφ. Note that for one qubit angle θ representation is in threedimensions. For multiple qubits θ representation is in higher orderdimensions.

Semiconductor Processing

Regarding semiconductor processing, numerous types of semiconductormaterial exist such as (1) single main atom types, e.g., Silicon (Si),Germanium (Ge), etc., and (2) compound material types, e.g.,Silicon-Germanium (SiGe), Indium-Phosphide (InP), Gallium-Arsenium(GaAs), etc.

A semiconductor layer is called intrinsic or undoped if no additionaldopant atoms are added to the base semiconductor crystal network. Adoped semiconductor layer is doped if other atoms (i.e. dopants) areadded to the base semiconductor crystal. The type of layer depends onthe concentration of dopant atoms that are added: (1) very low dopedsemiconductor layers having high resistivity, i.e. n-type denoted by n−−and p-type denoted by p−−, having resistivities above 100 Ohm·cm; (2)low doped semiconductor layers, i.e. p-type denoted with p- and n-typedenoted with n−, having resistivities around 10 Ohm·cm; (3) medium dopedlayers, i.e. p for p-type and n for n-type; (4) high doped layers, i.e.p+ and n+; and (5) very highly doped layers, i.e. p++ and n++.

Note that introducing dopants in a semiconductor crystal likely resultsin defects that introduce energy traps that capture mobile carriers.Traps are detrimental for semiconductor quantum structures because theycapture and interact with the quantum particles resulting in decoherenceof the quantum information. For realizing semiconductor quantumstructures undoped semiconductor layers are preferred.

Classic electronic devices use mostly low, medium, high and very highlydoped semiconductor layers. Some layers are ultra-highly doped to behaveas metals, such as the gate layer.

Semiconductor processing is typically performed on large semiconductorwafers which have a given thickness for mechanical stability. Circuitryis fabricated on a very thin layer on the top of the wafer where theunused thick portion of the wafer is termed the substrate. In a bulkprocess, devices are fabricated directly in the semiconductor body ofthe wafer.

An insulating layer (e.g., oxide) isolates from the substrate thedevices used to create circuitry. Semiconductor on insulator process,e.g., silicon on insulator (SOI), uses a layer of insulator (e.g.,oxide) between the thin top semiconductor layer where devices arerealized and the substrate.

To improve circuit performance, the wafer is processed such that thedevices are realized on top of an insulator substrate, e.g.,semiconductor-on-glass, semiconductor-on-organic material,semiconductor-on-sapphire, etc.

Alternatively, the semiconductor substrate is eliminated and replacedwith a nonelectrical conducting material such as a polymer or othermaterial compatible with a semiconductor process (e.g.,substrate-replacement processes). Substrate replacement in realizingsemiconductor quantum structures significantly reduces or eliminatessubstrate decoherence.

High resistivity (i.e. very low doped) substrates are the next bestsubstrate choice for semiconductor quantum structures. Althoughintrinsic substrates are also suitable for semiconductor quantumstructures, there are specific limitations that prevent the use ofintrinsic substrates.

Thus, in accordance with the invention, semiconductor quantum structurescan be realized in (1) bulk processes, (2) SOI processes, (3) substratereplacement processes, or (4) semiconductor on other materials.

Regarding processing, (1) planar processes may be used where layers havepredominantly one orientation, i.e. horizontal; and (2)three-dimensional processes (3D) allow layers with both horizontal andvertical orientation, realizing more complex 3D structures. It isappreciated that although layers are shown in the figures as rectangularprisms for simplicity, physically the layers have more complicatedstructures. For example, corners are often rounded and distortions arepresent due to the masking process. In depth dimension, layers tend tohave a trapezoidal shape instead of the ideal rectangular one. Thesemiconductor quantum structures of the present invention can berealized in either planar or 3D processes.

Quantum Computing System

A high-level block diagram illustrating a first example quantum computersystem constructed in accordance with the present invention is shown inFIG. 1. The quantum computer, generally referenced 10, comprises aconventional (i.e. not a quantum circuit) external support unit 12,software unit 20, cryostat unit 36, quantum processing unit 38, clockgeneration units 33, 35, and one or more communication busses betweenthe blocks. The external support unit 12 comprises operating system (OS)18 coupled to communication network 76 such as LAN, WAN, PAN, etc.,decision logic 16, and calibration block 14. Software unit 20 comprisescontrol block 22 and digital signal processor (DSP) 24 blocks incommunication with the OS 18, calibration engine/data block 26, andapplication programming interface (API) 28.

Quantum processing unit 38 comprises a plurality of quantum corecircuits 60, high speed interface 58, detectors/samplers/output buffers62, quantum error correction (QEC) 64, digital block 66, analog block68, correlated data sampler (CDS) 70 coupled to one or more analog todigital converters (ADCs) 74 as well as one or more digital to analogconverters (DACs, not shown), clock/divider/pulse generator circuit 42coupled to the output of clock generator 35 which comprises highfrequency (HF) generator 34. The quantum processing unit 38 furthercomprises serial peripheral interface (SPI) low speed interface 44,cryostat software block 46, microcode 48, command decoder 50, softwarestack 52, memory 54, and pattern generator 56. The clock generator 33comprises low frequency (LF) generator 30 and power amplifier (PA) 32,the output of which is input to the quantum processing unit (QPU) 38.Clock generator 33 also functions to aid in controlling the spin of thequantum particles in the quantum cores 60.

The cryostat unit 36 is the mechanical system that cools the QPU down tocryogenic temperatures. Typically, it is made from metal and it can befashioned to function as a cavity resonator 72. It is controlled bycooling unit control 40 via the external support unit 12. The coolingunit control 40 functions to set and regulate the temperature of thecryostat unit 36. By configuring the metal cavity appropriately, it ismade to resonate at a desired frequency. A clock is then driven via apower amplifier which is used to drive the resonator which creates amagnetic field. This magnetic field can function as an auxiliarymagnetic field to aid in controlling one or more quantum structures inthe quantum core.

The external support unit/software units may comprise any suitablecomputing device or platform such as an FPGA/SoC board. In oneembodiment, it comprises one or more general purpose CPU cores andoptionally one or more special purpose cores (e.g., DSP core, floatingpoint, etc.) that that interact with the software stack that drives thehardware, i.e. the QPU. The one or more general purpose cores executegeneral purpose opcodes while the special purpose cores executefunctions specific to their purpose. Main memory comprises dynamicrandom access memory (DRAM) or extended data out (EDO) memory, or othertypes of memory such as ROM, static RAM, flash, and non-volatile staticrandom access memory (NVSRAM), bubble memory, etc. The OS may compriseany suitable OS capable of running on the external support unit andsoftware units, e.g., Windows, MacOS, Linux, QNX, NetBSD, etc. Thesoftware stack includes the API, the calibration and management of thedata, and all the necessary controls to operate the external supportunit itself.

The clock generated by the high frequency clock generator 35 is input tothe clock divider 42 that functions to generate the signals that drivethe QPU. Low frequency clock signals are also input to and used by theQPU. A slow serial/parallel interface (SPI) 44 functions to handle thecontrol signals to configure the quantum operation in the QPU. The highspeed interface 58 is used to pump data from the classic computer, i.e.the external support unit, to the QPU. The data that the QPU operates onis provided by the external support unit.

Non-volatile memory may include various removable/non-removable,volatile/nonvolatile computer storage media, such as hard disk drivesthat reads from or writes to non-removable, nonvolatile magnetic media,a magnetic disk drive that reads from or writes to a removable,nonvolatile magnetic disk, an optical disk drive that reads from orwrites to a removable, nonvolatile optical disk such as a CD ROM orother optical media. Other removable/non-removable, volatile/nonvolatilecomputer storage media that can be used in the exemplary operatingenvironment include, but are not limited to, magnetic tape cassettes,flash memory cards, digital versatile disks, digital video tape, solidstate RAM, solid state ROM, and the like.

The computer may operate in a networked environment via connections toone or more remote computers. The remote computer may comprise apersonal computer (PC), server, router, network PC, peer device or othercommon network node, or another quantum computer, and typically includesmany or all of the elements described supra. Such networkingenvironments are commonplace in offices, enterprise-wide computernetworks, intranets and the Internet.

When used in a LAN networking environment, the computer is connected tothe LAN via network interface 76. When used in a WAN networkingenvironment, the computer includes a modem or other means forestablishing communications over the WAN, such as the Internet. Themodem, which may be internal or external, is connected to the system busvia user input interface, or other appropriate mechanism.

Computer program code for carrying out operations of the presentinvention may be written in any combination of one or more programminglanguages, including an object oriented programming language such asJava, Smalltalk, C++, C# or the like, conventional proceduralprogramming languages, such as the “C” programming language, andfunctional programming languages such as Python, Hotlab, Prolog andLisp, machine code, assembler or any other suitable programminglanguages.

Also shown in FIG. 1 is the optional data feedback loop between thequantum processing unit 38 and the external support unit 12 provided bythe partial quantum data read out. The quantum state is stored in thequbits of the one or more quantum cores 60. The detectors 62 function tomeasure/collapse/detect some of the qubits and provide a measured signalthrough appropriate buffering to the output ADC block 74. The resultingdigitized signal is sent to the decision logic block 16 of the externalsupport unit 12 which functions to reinject the read out data back intothe quantum state through the high speed interface 58 and quantuminitialization circuits. In an alternative embodiment, the output of theADC is fed back to the input of the QPU.

In one embodiment, quantum error correction (QEC) is performed via QECblock 64 to ensure no errors corrupt the read out data that isreinjected into the overall quantum state. Errors may occur in quantumcircuits due to noise or inaccuracies similarly to classic circuits.Periodic partial reading of the quantum state function to refresh allthe qubits in time such that they maintain their accuracy for relativelylong time intervals and allow the complex computations required by aquantum computing machine.

It is appreciated that the architecture disclosed herein can beimplemented in numerous types of quantum computing machines. Examplesinclude semiconductor quantum computers, superconducting quantumcomputers, magnetic resonance quantum computers, optical quantumcomputers, etc. Further, the qubits used by the quantum computers canhave any nature, including charge qubits, spin qubits, hybridspin-charge qubits, etc.

In one embodiment, the quantum structure disclosed herein is operativeto process a single particle at a time. In this case, the particle canbe in a state of quantum superposition, i.e. distributed between two ormore locations or charge qdots. In an alternative embodiment, thequantum structure processes two or more particles at the same time thathave related spins. In such a structure, the entanglement between two ormore particles could be realized. Complex quantum computations can berealized with such a quantum interaction gate/structure or circuit.

In alternative embodiments, the quantum structure processes (1) two ormore particles at the same time having opposite spin, or (2) two or moreparticles having opposite spins but in different or alternate operationcycles at different times. In the latter embodiment, detection isperformed for each spin type separately.

A high level block diagram illustrating a generalized quantum structureinterfaced to classical integrated electronic control circuitry is shownin FIG. 2. The example quantum circuit, generally referenced 80,comprises quantum structure 84 at its core, and support circuitry thatin one embodiment is integrated on the same physical realized support orexternal on a different physical realized support. The support circuitrycomprises reset circuits 82 for flushing the quantum structure of anyavailable free carriers before starting the quantum operation and toprepare it for a new quantum operation, injector circuits 88 thatfunction to inject one or more particles into the quantum corestructure, imposer circuits 90 that control the quantum operation andthe flow of the quantum computation between the injected particles,detector circuits 86 that sense whether a particle is present or not inthe output qdots and the particles at the output points of the quantumstructure after the quantum operation has been performed, and controlcircuitry 92. Note that in one embodiment, multiple such quantumstructures/quantum cores can be interconnected and/or operated inparallel. Further note that the common electrical node of the resetcircuit 82 output and the injector circuit 88 output can be the same asthe electrical node of the detector circuit (86) input. In this case,the three circuits time-share their active operations.

To achieve quantum operation, physical structures must be cooled tocryogenic temperatures and be isolated as much as possible fromenvironmental perturbations (e.g., external electric fields and/ormagnetic fields, etc.). To perform quantum computing using particles ina semiconductor structure, the particles (e.g., electrons, holes, etc.)need to be able to be excited in quantum states and to stay in suchstates for a long enough time for the operation and measurement of thequantum operation to be realized. At higher temperatures, the thermalenergy of the particle results in the decoherence of its quantum state.

In one embodiment, the semiconductor based quantum structure uses acontinuous well with an imposing gate that generates a controlled localdepletion region to separate two or more regions of the well that formquantum dots (qdots). By modulating the potential of the imposer gate,controlled tunneling through the local depleted region is enabledbetween the plurality of sections of the continuous well, realizing thefunction of a position/charge qubit. It is appreciated that more complexstructures having a higher number of qdots per continuous well and alarger number of wells can be built using the techniques of the presentinvention. Both planar and 3D semiconductor processes can be used tobuild such well-to-well tunneling quantum structures. By combining anumber of such elementary quantum structures/gates, a quantum computingmachine is realized.

Quantum Operation

To aid in understanding the principles of the present invention, a briefexplanation of quantum operation is presented below.

As stated supra, in classic electronics, the unit of information is abit that can represent only one of the two states “0” and “1” at a giventime. Computations in classical computers are performed sequentially andevery bit can hold only one state at a time.

As stated supra, quantum electronics uses the quantum behavior ofparticles to perform computations. The unit of quantum information is aquantum bit or qubit. A qubit has two or more base states denoted by{circumflex over (0)} and {circumflex over (1)} (or |0> and |1>) but incontrast with a classic bit, a qubit can be in a superposed state thatcontains some percentage ‘a’ of state {circumflex over (0)}, and somepercentage ‘b’ of state {circumflex over (1)}, denoted by a{circumflexover (0)}+b{circumflex over (1)}. Since a qubit in quantum structurescan simultaneously be in multiple superposed states, multiple sets ofcomputations can be performed concurrently, resulting in large quantumcomputation speed-ups, when compared with classic computations.

A quantum particle is described by its position and/or spin. Theparticles used in quantum structures are called quantum particles. Thereare qubits based on the quantum position of the particles, also namedcharge-qubits, while other qubits use the spin of the quantum particles,also named spin-qubits. In quantum structures, the charge carriers areheld in specific regions called quantum dots or qdots. A quantumstructure is constructed from one or more qdots.

Performing a quantum computation involves several steps. First thestructure needs to be reset, which means that all the free carriers(e.g., electrons or holes) from the structure need to be flushed out.Once the free carriers are removed, the structure is initialized meaningparticles are introduced in one of the base states (e.g., {circumflexover (0)} or {circumflex over (1)}). In the case of a charge-qubit(position-qubit) it means that a carrier is loaded in one of the qdots.A free carrier not coming from the quantum initialization process caninteract with the quantum particles and result in decoherence, i.e. lossof quantum information. After the particles have been loaded in thecorresponding base states they undergo the desired quantum operationunder control of gate control terminals. Once the desired quantumoperations are complete a detection is performed whereby the presence orabsence of a particle in a given qdot at a given time is tested.Detection is usually destructive which means that the quantum particle'swavefunction and its state collapse. Special nondestructivedetection/measurement exist that do not collapse the quantum state. Insuch cases, multiple measurements of the same quantum state can beperformed.

The position of a quantum particle is given by the region where theparticle wave-function is mostly present. In one embodiment, quantumstructures use semiconductor qdots realized with semiconductor wellswhere the particle transport is done through tunneling which is aquantum effect. The tunneling or particle transport is controlled bycontrol terminals. In one embodiment, the control terminals are realizedusing gates but they may comprise other semiconductor process layers.

To illustrate, consider a generic position double qdot structure havinga “dog bone” shape shown in FIG. 3A. The structure comprises a controlgate 974 giving rise to two qdots 970, 972, that correspond to the |0>and |1> base states, or “left” and “right” base states, when anelectrostatic particle happens to be there. Higher order positionquantum structures can be realized having more than two base states andthus use more than two qdots. The particle transport from one qdot tothe other is done through tunneling. Before initialization both qdotsmust be cleared of quantum particles since a reset flushes out all freecarriers.

Note that a key difference between the classic and quantumstructures/circuits is that the structure can not only be in the basestates |0> and |1>, but also in a superposed position a|0>+b|1>, with aconstraint |a|²+|b|²=1, meaning the particle is present simultaneouslyin both qdots of the structure. When the signal on the control terminalcauses a lowering of the tunneling barrier, the particle initiallyloaded in the left qdot 970 will tunnel to the right qdot 972. Theposition of the particle and thus the corresponding quantum state isgiven by the pulse width of the signal V_(control) applied to thecontrol gate. If the pulse width is long enough, after the particle hastunneled to the right qdot 972 it will tunnel back to the left qdot 970and then again to the right qdot 972 and the process repeats itself inan oscillatory fashion. The period of this oscillation, called the Rabioscillation (especially in case of a time-dependent Hamiltonian),depends on the tunnel current and thus on the control signal V_(control)applied and the configuration and process of the specific structure. Thetime needed for a particle to tunnel forward and then back to itsinitial position is called the Rabi period.

The Rabi oscillation after reset but before initialization is shown inFIG. 3B where waveform 976 represents an ideal oscillation and waveform978 represents oscillation with some amount of decoherence or leakage ofwavefunction.

Consider a quantum particle 976 loaded in the left qdot 970 with a basestate |0>, as shown in FIG. 3C. The Rabi oscillation waveform atinitialization (dot referenced 980) is shown in FIG. 3D. In ahorizontally oriented double qdot, a quantum particle 976 loaded in theright qdot 972 is considered in the base state |1>, as shown in FIG. 3E.Similarly, the up and down qdots correspond to the |0> and |1> basestates in a vertically oriented double qdot. The control terminal(typically the gate) determines the height of the tunnel barrier. If thepotential barrier is high then tunneling is blocked (i.e. negligible).On the other hand, if the potential barrier is low then tunneling isallowed and the particle moves from one qdot to the other, resulting ina change in quantum state.

If the control signal pulse width is equal to half the Rabi period asshown in FIG. 3F, then the particle will tunnel from the left qdot 970to the right qdot 972, i.e. transition from the |0> base state to the|1> base state also known as a quantum inversion, trajectory of which isrepresented by waveform solid portion 982.

If the control pulse width is equal to one quarter of the Rabi period asrepresented by waveform solid portion 984 trajectory in FIG. 3H, thenthe particle will be present equally in the left qdot 970 and in theright qdot 972 as shown in FIG. 3G. This equal distribution quantumstate is called the Hadamard state and is fundamental for quantumcomputation. The double qdot with a quarter Rabi period control signalperforms the function of a fundamental Hadamard quantum gate.Considering the sinewave of an oscillatory effect, the Hadamard statecorresponds to the zero crossings, while the peak of the positive cyclecorresponds to the base state |0> and the peak of the negative cyclecorresponds to the base state |1>. All points between the positive andnegative peaks correspond to superposition states.

If the pulse width of the control signal is less than one quarter theRabi period as represented by solid waveform portion 986 in FIG. 3J,then the quantum particle is split between the two qdots as shown inFIG. 3I but it will have a larger presence in the left qdot 970 versusthe right qdot 972. Similarly, if the pulse width is larger than onequarter the Rabi period as represented by solid waveform portion 988 inFIG. 3L, than the quantum particle is split as shown in FIG. 3K but willhave a larger presence in the right qdot 972.

If the position of the particle is represented as a vector of constantlength in a circular coordinate system, a vector pointing up representsthe |0> base state, while a vector pointing down represents the |1> basestate. Any other position is a superposed state that constitutes aquantum rotation operation. As such the double qdot quantum structurewith a variable control signal pulse width constitutes a controlledquantum rotation gate.

The initialization of a quantum structure is realized by an interfacedevice (described in more detail infra) having one side connected toclassical circuitry and the other side connected to quantum circuitry,i.e. half classic, half quantum. On the classic side, the carriers(e.g., electrons or holes) have a collective behavior, sometimes calleda sea of electrons (or holes). On the quantum side, the carriers exhibitsingle charge carrier or a few carrier behavior and their interaction isbased on the laws of quantum mechanics. Injecting exactly a singleparticle in the quantum structure at a given qdot can be realizedthrough the tunneling effect in the interface device. Once a singleparticle has tunneled, the electric field changes such that it opposesthe tunneling of a subsequent particle. Such behavior of the interfacedevice is critical to be able to inject one or multiple particles intoone or multiple qdots of a given quantum structure.

The pulse width of the control signals can be digitally controlled onthe classical side of the circuits and thus determine what kind ofquantum operation is performed, resulting in a programmable quantummachine. In this case, the same hardware implementation is able toperform different quantum operations based on the specific controlsignal applied.

Note that each quantum particle injected into the quantum structurerepresents a qubit. In the position qubit at least two qdots are neededto implement a qubit. In the general case, structures with N qubits andM qdots can be constructed. The number of injectors, however, should beequal to N if all particles are injected at the same time, or it can belower than N if the particles are injected at different times.

A diagram illustrating a circular shaped semiconductor quantum structureincorporating local depleted well tunneling is shown in FIG. 4A. Thequantum structure, generally referenced 100, comprises a continuous wellwith a local depleted region with a control gate 106 fabricated over itthat functions to separate the well into two or more portions eachimplementing a qdot. In this example, the continuous well is split intotwo qdots 102, 104 with a tunneling path 108 formed between them for thequantum particle 110, e.g., electron, to tunnel through. The tunnelingpath 108 is considered to effectively connect the two wells 102 and 104in a quantum manner. The quantum operation is controlled by the gate 106fabricated over the tunneling path 108. The gate functions to modulatethe energy barrier created by the local depleted region. The twosections of the well, the tunneling path with the local depleted region,and the control gate can take any number of different shapes (describedinfra) allowed by the particular semiconductor process used (planar or3D).

In one embodiment, the two qdots 102, 104 are linked by a region 108that is partially or completely locally depleted and in which tunnelingoccurs as indicated by arrow 109 through the tunneling path. The controlgate typically overlaps the tunneling path in order to maintainwell-controlled depletion of the entire linking region between the twoqdots. This prevents direct electric conduction between the two qdots.

The depletion region is required for quantum operation of the structure.If there were no depletion region, the operation would revert to aclassical transistor operation in on/off modes and the particle cannormally move from one side to the other. Note that the probability of aparticle tunneling through the depletion region is approximatelyexponentially linked to the width of the depletion region. If thedepletion region is very narrow, the particle will tunnel and thequantum operation is achieved. If the depletion region is wide, thenthere is no tunneling or the tunneling is so weak that it can beneglected. This is also dependent on the tunneling barrier height. For ap-type semiconductor material, placing a positive potential on the gatewill repel the holes and create a depletion region. Note that thevoltage is necessarily lower than the level that results in the creationof an inversion channel.

The control signals that need to be applied to the gate depend onwhether the semiconductor material is p or n type. Consider for examplep-type semiconductor material, with no potential on the gate, theparticle may be free to tunnel. Placing a positive potential on the gatewill repel the particles (i.e. holes) and create the depletion regionthereby hindering tunneling. If the potential on the gate is removed orbrought closer to zero to zero or made negative, the particles arepermitted to tunnel in relation to the potential applied. The operationof the quantum structure is significantly different than that of aconventional transistor.

In one embodiment, the two qdots 102, 104 are realized by a singlesemiconductor well having a polysilicon gate on top. The tunnelinghappens laterally or horizontally through the depleted region thatisolates the two qdots.

Note also that in one embodiment the well is surrounded by oxide,isolating layers, and/or one or more wide depletion regions that preventthe quantum particle from escaping from the well.

A diagram illustrating the change in the aperture tunnel barrier from awide depletion region to a narrow depletion region is shown in FIG. 4B.To contain or trap the quantum particle 114, the barrier potential 112between the two wells is made high (dashed line 116). Lowering thebarrier potential between the two wells (solid line below the dashedline) enables the quantum particle to tunnel from one qdot to the other.

A diagram illustrating a first rectangular shaped semiconductor quantumstructure incorporating local depleted well tunneling is shown in FIG.4C. The quantum structure, generally referenced 120, is similar tostructure 100 of FIG. 4A apart from the dog bone shape of the continuouslocal depleted well. Control gate 126 is fabricated over the well andfunctions to separate the well into two qdots 122, 124 with tunnelingpath 128 formed between them for the quantum particle 130 to tunnelthrough. The quantum operation is controlled by the gate 126 fabricatedover the tunneling path 128. The gate functions to modulate the barriercreated by the local depleted region.

The two qdots 122, 124 are linked by a region 128 that is partially orcompletely locally depleted and in which tunneling occurs as indicatedby arrow 129 through the tunneling path. The control gate typicallyoverlaps the tunneling path in order to maintain well-controlleddepletion of the entire linking region between the two Qdots. Thisprevents direct electric conduction between the two qdots.

A diagram illustrating the change in the aperture tunnel barrier from awide depletion region to a narrow depletion region is shown in FIG. 4D.To contain or trap the quantum particle 134, the barrier potential 132between the two wells is made high (dashed line 136). Lowering thebarrier potential (solid line) enables the quantum particle to tunnelfrom one qdot to the other.

A diagram illustrating a second rectangular shaped semiconductor quantumstructure incorporating local depleted well tunneling is shown in FIG.5. The quantum structure, generally referenced 140, is similar tostructure 100 of FIG. 4A apart from the ‘S’ shape of the continuous wellwith local depleted region. Control gate 146 is fabricated over the welland functions to separate the well into two qdots 142, 144 withtunneling path 148 formed between them for the quantum particle 149 totunnel through. The quantum operation is controlled by the gate 146fabricated over the tunneling path 148. The gate functions to modulatethe barrier created by the local depleted region.

The two qdots 142, 144 are linked by a region 148 that is partially orcompletely locally depleted and in which tunneling occurs as indicatedby arrow 147 through the tunneling path. The control gate typicallyoverlaps the tunneling path in order to maintain well-controlleddepletion of the entire linking region between the two Qdots. Thisprevents direct electric conduction between the two qdots.

A diagram illustrating a cross section of an example semiconductorquantum structure 150 is shown in FIG. 6. An exemplary cross section ina silicon-on-insulator (SOI) process is shown in which the substrate 152is low doped (i.e. high resistivity) and is isolated from the quantumdevice with a buried oxide layer (BOX) 154. This reduces the decoherenceof the quantum particle. In one embodiment, the semiconductor quantumdevice employs tunneling through the local depleted region. In anotherembodiment, tunneling occurs through the oxide layer between thesemiconductor well 160 (low doped or undoped) and the partiallyoverlapping gate 158 and oxide layer 166. The active layer 160 isisolated using oxide from adjacent structures, e.g., shallow trenchisolation (STI) 156, reducing further the quantum particle decoherence.

Note that the substrate may comprise (1) a semiconductor, (2) silicon oninsulator (SOI) substrate, where the substrate comprises sapphire,glass, organic material, etc., (3) an insulating substrate replacement,for example, sapphire, glass, organic material, plastic, polymer, etc.,or (4) any other insulating material compatible with a semiconductorprocess.

Note that regardless of the substrate used, the quantum structure mustbe electrically isolated from the substrate for the structure to operateproperly. Otherwise, the quantum particle may escape thus preventingquantum operation of the structure.

Several ways to electrically isolate the quantum structure include: (1)utilizing an SOI or low doped substrate where the oxide layerelectrically isolates the quantum structure from the substrate; (2)using substrate replacement such as an insulator material, e.g.,polymer, glass, etc.; and (3) using a fixed depletion region, as thequantum particle can tunnel only through a relatively narrow insulatingregion such as very thin oxide or a thin depletion region. If thedepletion region is too wide, the quantum particle is prevented fromtraveling. Note that this last option can be fabricated using bulkprocesses.

The quantum operation is controlled by the gate located over thetunneling path that modulates the barrier created by the local depletionregion.

In one embodiment, a low doped substrate interacts with the quantumparticle with far and weak interactions. Tunneling of the quantumparticle 162 occurs in region 164 between the two qdots formed in theactive layer 160 and the tunnel path may be straight through from oneqdot to the other (see dashed arrow 168) or may take a path through thegate and back to the active layer (see dashed arrow 169). Alternatively,the substrate may comprise a substrate replacement that includesnon-conducting material, e.g., polymer, glass, sapphire, without freecharge or ions that can interact with the quantum particle.

In both cases, the active well is preferably isolated on all sides (i.e.typically with oxide) where the particles are permitted to travel onlythrough a narrow link where tunneling occurs.

Alternatively, bulk semiconductor processes are used where the substrate152 is isolated from the quantum device using a large depleted regionunder the quantum gate instead of BOX. In another alternativeembodiment, the quantum device is placed directly into the substrate.The quantum device can be isolated laterally from other devices usingoxide layers 156 (e.g., STI or another preferably low doped well). Inanother alternative embodiment, a bulk semiconductor quantum structurereplaces the substrate with an isolator material 152 having no freecarriers or ions that can interact with the quantum particle. In analternative embodiment, a substrate replacement process or asemiconductor on insulator process can also be used.

The cross section 150 shows the quantum structure with well-to-welltunneling through the local depleted region. It is noted that if thedepleted region 164 is wide, then no or negligible tunneling 168 ispresent. If under the control of the gate the tunneling barrier islowered and the depletion region gets narrower, a sizeable tunnelingcurrent may occur, resulting in the quantum particle tunneling from oneqdot to the other.

Note that tunneling is also possible from the well to the gate and thenfrom the gate to the adjacent well, bypassing the local depleted area(arrow 169). The width of the depleted area, however, can be madenarrower than the thin gate oxide and thus the predominant tunneling canbe made to be through the local depleted region.

In some cases, the gate oxide thickness is reduced using specialmaterials such as hafnium oxide. The tunneling barrier height, however,is still high and tunneling is likely to happen through the depletionlayer.

In accordance with the present invention, the quantum structure maycomprise numerous shapes and sizes constrained only by design rule check(DRC) of the particular semiconductor process used to fabricate thestructure. Several examples of quantum structure shapes, e.g., circles,squares, rectangles, polygons, etc. will now be described. In each case,these shapes can be used for the constituent layers and for one or moreqdots making up the quantum structure.

A double qdot quantum structure which is the elementary structure forposition qubit quantum computing contains two quantum dots and atunneling path (often narrow) between them.

Quantum Structure Shapes

A diagram illustrating an example circular shape 170 for the quantumstructure of the present invention is shown in FIG. 7A. A diagramillustrating an example square shape 172 for the quantum structure ofthe present invention is shown in FIG. 7B. A diagram illustrating anexample square shape with rounded corners 174 for the quantum structureof the present invention is shown in FIG. 7C. A diagram illustrating anexample hexagonal shape 176 for the quantum structure of the presentinvention is shown in FIG. 7D. A diagram illustrating an examplerectangular shape 178 for the quantum structure of the present inventionis shown in FIG. 7E.

A diagram illustrating an example trapezoidal shape 180 for the quantumstructure of the present invention is shown in FIG. 7F. A diagramillustrating a first example overlapping square shape 182 for thequantum structure of the present invention is shown in FIG. 7G. Adiagram illustrating a first example ‘L’ shape 184 for the quantumstructure of the present invention is shown in FIG. 7H. A diagramillustrating an example ‘S’ shape 186 for the quantum structure of thepresent invention is shown in FIG. 7I. A diagram illustrating a secondexample ‘L’ shape 188 for the quantum structure of the present inventionis shown in FIG. 7J.

A diagram illustrating an example barely touching squares shape 189 forthe quantum structure of the present invention is shown in FIG. 7K. Notethat in this example shape and others it is preferable that the squaresoverlap as little as possible since it is desirable to have as narrow atunneling region as possible to maximize control. A large tunneling areais more difficult to control and to deplete sufficiently to preventpartial or complete tunneling.

A diagram illustrating an example barely touching square shape 190 withoptical proximity control 192 for the quantum structure of the presentinvention is shown in FIG. 7L. A diagram illustrating an example doublesquares 194 with narrow neck 196 shape for the quantum structure of thepresent invention is shown in FIG. 7M. A diagram illustrating a secondexample overlapping square shape 198 for the quantum structure of thepresent invention is shown in FIG. 7N. A diagram illustrating a thirdexample overlapping square shape 200 for the quantum structure of thepresent invention is shown in FIG. 7O.

A diagram illustrating an example barely touching rectangular shape 202for the quantum structure of the present invention is shown in FIG. 7P.A diagram illustrating an example barely touching double overlappingsquares shape 222 for the quantum structure of the present invention isshown in FIG. 7Q. A diagram illustrating an example double squaresconnected via single smaller square shape 208 for the quantum structureof the present invention is shown in FIG. 7R. A diagram illustrating anexample double squares connected via double smaller squares shape 204for the quantum structure of the present invention is shown in FIG. 7S.

Several alternative ways of imposing the potential on the control gatewill now be described. For illustration purposes only, doubleoverlapping square shapes are used for the qdots. It is appreciated thatother shapes may be used with each technique without departing from thescope of the invention. Note that the width of the tunneling section ofthe continuous well in each case is preferably as small as possible, butcan vary in size based on the given DRC of the semiconductor processused.

Control Gate

A diagram illustrating a first example control gate for the quantumstructure of the present invention is shown in FIG. 8A. The quantumstructure, generally referenced 220, comprises a floating control gate226 with an adjacent gate 222 that is in close proximity thereto thatimposes potential to the gate 226 of the double overlapping squareshaped qdots 224 with tunnel path 228. Note that changing the potentialof the overlapping control gate is operative to modulate the tunnelbarrier height.

A diagram illustrating a second example control gate for the quantumstructure of the present invention is shown in FIG. 8B. The quantumstructure, generally referenced 230, comprises a metal control gate 232imposing on the floating control gate 234 using adjacent or overlappositioning over the control gate 234 of the double overlapping squareshaped qdots 236 with tunnel path 238.

A diagram illustrating a third example control gate for the quantumstructure of the present invention is shown in FIG. 8C. The quantumstructure, generally referenced 240, comprises a contact 244 from ametal feed 242 to a control gate 246 over double overlapping squareshaped qdots 248 with tunnel path 249. The control gate is drivendirectly with an electrical signal (e.g., pulsed electric signal).

Quantum Structures With Control Gates

As described supra, the quantum structure may comprise numerous shapesand sizes constrained only by design rule check (DRC) of the particularsemiconductor process used to fabricate the structure. Several examplesof quantum structures having one or more control gates will now bedescribed. It is important to note that there is a difference betweenthe shapes drawn in the figures and the physical realized shapes.Further, several factors such as the semiconductor process usedcontribute to determining the physical shapes realized. Note also thatin most cases, the link channel is mandatory for the quantum structuresemploying tunneling through the depletion region. The link channel,however, may not be present on the layers drawn in the figures.

Each semiconductor quantum structure disclosed uses well-to-welltunneling through a local depleted region. In order to exercise goodcontrol over the tunneling effect, the tunneling path section of thewell is preferably relatively narrow when compared with the dimensionsof the rest of the well that constitutes the qdots. A gate is placed ontop of the tunneling path section of the well in which the localdepleted region is induced. A complete overlap of the control gate onthe tunneling path is preferable in order to have good control over theentire width of the tunneling path and achieve reliable isolationbetween the two or more sections of the continuous well that implementsthe quantum dots. The potential on the control gate functions tomodulate the width of the local depletion region and to control thetunneling between the two adjacent sections of the well that representtwo separate qdots (i.e. well-to-well tunneling). As described supra,this potential is imposed, for example, by another metal layer with nocontact to gate 226 (i.e. a floating gate) as shown in FIG. 8A or with ametal layer contacted to the gate (i.e. directly driven gate) as shownin FIG. 8C. The overlapping gate is positioned such that a smalleroverlap with the two adjacent sections of the well is realized resultingin a larger Coulomb blockade voltage.

A diagram illustrating an example quantum structure with double squarecorner touching shape is shown in FIG. 9A. The quantum structure,generally referenced 250, comprises a continuous well with control gate254 placed over edge portions 251, 253 of the square shapes to form twoqdot regions 252.

A diagram illustrating an example quantum structure with double squareshape and optical proximity control is shown in FIG. 9B. The quantumstructure, generally referenced 260, comprises a continuous well withcontrol gate 264 placed over edge portions of the square shapes to formtwo qdot regions 262. Optical proximity control 266 is used to improvethe tunnel path. As is known in the semiconductor processing arts,optical proximity correction can be used within the vicinity of thelocal depleted tunneling well to aid in improving the resultingstructures fabricated on the substrate. Note that optical proximitycorrection techniques may be used with any of the structures disclosedin this document to improve the resulting structures. Note that thesquares 266 shown only exist on one or more masks used in thefabrication of the structure and do not reflect any structures actuallybuilt on the substrate. These squares, however, typically have an effecton the shape of such structures constructed nearby. The desired effectsinclude width and length adjustments of the tunneling path.

Note that in general, nanometer semiconductor processes natively yielddistortions around corners and the narrow features. Optical correctionhelps realize physical shapes close to the desired shapes.

A diagram illustrating an example quantum structure with double squareand narrow neck shape is shown in FIG. 9C. The quantum structure,generally referenced 270, comprises a continuous well with control gate274 placed over narrow tunnel path 276 and edge portions of the squareshapes to form two qdot regions 272.

A diagram illustrating a first example quantum structure with doubleoverlapping square shape is shown in FIG. 9D. The quantum structure,generally referenced 280, comprises a continuous well with control gate284 placed over narrow tunnel path 286 (but wider than tunnel path 296in FIG. 9E) and edge portions of the square shapes to form two qdotregions 282.

A diagram illustrating a second example quantum structure with doubleoverlapping square shape is shown in FIG. 9E. The quantum structure,generally referenced 290, comprises a continuous well with control gate294 placed over narrow tunnel path 296 and edge portions of the squareshapes to form two qdot regions 292.

A diagram illustrating an example quantum structure with ‘L’ shape isshown in FIG. 9F. The quantum structure, generally referenced 300,comprises a continuous well with control gate 304 placed over thetransition portion of the rectangular shapes to form two qdot regions302.

A diagram illustrating an example quantum structure with double roundedbarely touching square shape is shown in FIG. 9G. The quantum structure,generally referenced 310, comprises a continuous well with control gate314 placed over narrow tunnel path 316 and edge portions of the roundedsquare shapes to form two qdot regions 312.

A diagram illustrating an example quantum structure with doublerectangular shape is shown in FIG. 9H. The quantum structure, generallyreferenced 320, comprises a continuous well with control gate 324 placedover narrow tunnel path 326 and edge portions of the rectangular shapesto form two qdot regions 322.

A diagram illustrating an example quantum structure with double squareconnected via double smaller square shape is shown in FIG. 9I. Opticalproximity correction is used here to turn the small feature connectingshapes into a narrow continuous link channel. The quantum structure,generally referenced 330, comprises a continuous well with control gate334 placed over double small square tunnel path 336 and edge portions ofthe square shapes to form two qdot regions 332.

A diagram illustrating an example quantum structure with double roundedsquare with narrow neck shape is shown in FIG. 9J. The quantumstructure, generally referenced 340, comprises a continuous well withcontrol gate 344 placed over contoured narrow tunnel path 346 and edgeportions of the rounded square shapes to form two qdot regions 342.

A diagram illustrating an example quantum structure with an overlappingpair of double rounded squares with narrow neck shape is shown in FIG.9K. The quantum structure, generally referenced 350, comprises acontinuous well with two control gates 354 placed over a contourednarrow tunnel path 356 and edge portions of the rounded square shapes toform three qdot regions 352. Note that the middle qdot is longer, beingcomprised of two semiconductor squares.

A diagram illustrating a first example quantum structure with a pair ofbarely touching double overlapping square shape is shown in FIG. 9L. Thequantum structure, generally referenced 360, comprises a continuous wellwith control gate 364 placed over tunnel path 366 and edge portions ofthe double square shapes to form two qdot regions 362.

A diagram illustrating a second example quantum structure with a pair ofdouble corner overlapping square shape is shown in FIG. 9M. The quantumstructure, generally referenced 370, comprises a continuous well withtwo floating control gates 374 with adjacent imposing gate potentialplaced over tunnel paths 378 and edge portions of the square shapes toform three qdot regions 372. Note that the middle qdot is formed by twosquares of active silicon.

A diagram illustrating a first example quantum structure with a doublesquare shape with narrow neck and butterfly shaped control gate is shownin FIG. 9N. Note that most of the quantum structures described supracomprise square or rectangular shaped gates. Some availablesemiconductor processes, however, allow for composed shapes for thegate. In these cases, both the well and the gate have a narrowconnecting channel. The quantum structure, generally referenced 380,comprises a continuous well with control gate 382 placed over narrowtunnel path 386 to form two qdot regions 384. Here, the gate and thewell both have narrow connecting channels. This structure results in amuch smaller gate to well overlap resulting in a much higher Coulombblockade voltage for the structure. This enables a higher performance ofthe quantum structure since a larger signal to noise ratio is achieved.

A diagram illustrating a second example quantum structure with a doublesquare shape with narrow neck and butterfly shaped control gate is shownin FIG. 9O. Similar to the structure of FIG. 9N, the quantum structure,generally referenced 390, comprises a continuous well with control gate392 placed over contoured narrow necked tunnel path 396 to form tworounded square qdot regions 392. Here too, the gate and the well bothhave narrow connecting channels.

A diagram illustrating an example quantum structure with a pair ofoverlapping double square shapes with narrow neck and butterfly shapedcontrol gates is shown in FIG. 9P. The quantum structure, generallyreferenced 400, comprises a continuous well with two floating controlgates 402 electrostatically coupled to adjacent imposing gates 406placed over contoured narrow necked tunnel paths 408 to form threerounded square qdot regions 404 with the gates 406 and the wells havingnarrow connecting channels.

A diagram illustrating an example conventional field effect transistor(FET) with drain and source doped diffusion and contacts is shown inFIG. 9Q. Using a conventional field effect transistor (FET) structure tobuild semiconductor quantum structures results in significantly degradedperformance. In one embodiment, a modified semiconductor process is usedto construct optimized semiconductor quantum structures.

Conventional wells have rectangular shapes disposed parallel to eachother. In one embodiment, the quantum structure uses (1) staircase wellshapes that provide pairs of locations where the interaction betweenquantum particles/states is very strong and (2) other pairs of locationsthat have weak or negligible interaction between the particles situatedat those locations.

The conventional FET structure, generally referenced 410, comprisesdrain and source doped diffusion with contacts 412 with metal on top,and gate 416 with contacts 414. This structure results in significantlyhigher parasitic gate capacitance since it includes the gate-to-metal,gate-to-contact and gate-to diffusion additional components. Note thatin classic FET structures, carriers move either through drift under anexternal electric field or through diffusion due to a gradient ofconcentration. An inversion channel is created by a relatively largegate voltage.

A diagram illustrating an example half conventional FET and half(potentially) quantum structure is shown in FIG. 9R. In accordance withthe present invention, a modified semiconductor process enables anactive layer without any diffusion, contact and metal on top. Thestructure, generally referenced 420, comprises a conventional doped side422 with diffusion contacts, an undoped or lightly doped quantum side426, and gate 427 with contacts 424. Such a structure has ahalf-classic, half-quantum structure with one side of the gate withoutany n or p doping and without contacts. This type of device can be used,for example, at the interface between classic circuits and quantumcircuits. In this case, the carriers move through tunneling from theclassic side to the quantum side.

A diagram illustrating an example quantum structure with rectangularshaped wells is shown in FIG. 9S. The full quantum structure, generallyreferenced 430, does not have any n or p doping or contacts on eitherside. Both sides 432 of the gate 436 with contacts 434 have the sameactive layer width which is approximately equal to the gate width. Thisresults in a larger gate capacitance. To reduce the parasitic gatecapacitance, the width of the active layer may be made smaller than thegate width on one or both sides.

A diagram illustrating an example quantum structure with dissimilarrectangular shaped wells is shown in FIG. 9T. The structure, generallyreferenced 440, comprises an asymmetric aperture tunneling well withgate 446 and gate contacts 448 placed thereover to generate two qdots442, 444 with reduced parasitic capacitance on the right side qdot.

A diagram illustrating an example quantum structure with offsetrectangular shaped wells is shown in FIG. 9U. The structure, generallyreferenced 450, comprises an asymmetric aperture tunneling well withgate 456 and gate contacts 458 placed thereover to generate two qdots452, 454 with both qdots having reduced parasitic capacitance.

Using active wells having different widths on the both sides of the gatereduces the parasitic gate capacitance. A more significant reduction ingate capacitance can be achieved, however, by having an active wellstructure having a narrow region under the gate and wider regions oneither side of the gate.

A diagram illustrating a first example quantum structure with spacedapart rectangular shaped wells is shown in FIG. 9V. The structure,generally referenced 460, comprises a symmetric dog bone aperturetunneling well with gate 466 having gate contacts 468 placed thereoverto generate two qdots 462, 464 with reduced parasitic capacitance onboth sides. Note, however, that there remains a residual overlap of thegate and the wider active wells on the two sides of the gate. Note thatthe aperture refers to the narrowed link channel between the two widerwell regions.

A diagram illustrating a first example quantum structure with spacedapart rectangular shaped wells offset from each other is shown in FIG.9W. The structure, generally referenced 470, comprises an asymmetric dogbone aperture tunneling well with gate 476 and gate contacts 478 placedthereover to generate two qdots 472, 474 with reduced parasiticcapacitance on both sides. Note, however, that there remains a residualoverlap of the gate and the wider active wells on the two sides of thegate.

In one embodiment, to further reduce gate capacitance the overlapbetween the gate and the wider wells on the sides are eliminated. Adiagram illustrating a second example quantum structure with spacedapart rectangular shaped wells is shown in FIG. 9X. The structure,generally referenced 480, comprises a symmetric dog bone aperturetunneling well with gate 486 and gate contacts 488 placed thereover togenerate two qdots 482, 484 with reduced parasitic capacitance on bothsides and no well-gate overlap in the wider regions.

A diagram illustrating a second example quantum structure with spacedapart rectangular shaped wells offset from each other is shown in FIG.9Y. The structure, generally referenced 490, comprises an asymmetric dogbone aperture tunneling well with gate 496 and gate contacts 498 placedthereover to generate two qdots 492, 494 with reduced parasiticcapacitance on both sides and no well-gate overlap in the wider regions.

As described supra, the quantum structure may be symmetric orasymmetric. The “dog-bone” quantum structure has some overhang of thewider wells passed the edge of the narrow link. The asymmetric dog bonequantum structure does not have any overhang on the narrow link side. Adiagram illustrating a third example quantum structure with spaced apartrectangular shaped wells offset from each other is shown in FIG. 9Z. Thestructure, generally referenced 500, comprises an asymmetric dog boneaperture tunneling well with partial overlap of the gate on the widewells and overhang passed the narrow link edges, and with gate 506 andgate contacts 508 placed thereover to generate two qdots 502, 504.

A diagram illustrating a fourth example quantum structure with spacedapart rectangular shaped wells offset from each other is shown in FIG.9AA. The structure, generally referenced 510, comprises an asymmetricdog bone aperture tunneling well with partial overlap of the gate on thewide wells and overhang passed the narrow link edges, and with gate 516and gate contacts 518 placed thereover to generate two qdots 512, 514with increased gate to well capacitance, but which may ease thefabrication process.

Narrow links between the two wider wells may be realized without havingthem drawn as such. In one embodiment, two wells have a punctual drawncontact but during fabrication a narrow link channel is formed betweenthe two wells using optical proximity correction. A diagram illustratinga first example quantum structure with corner abutting rectangularshaped wells is shown in FIG. 9AB. The structure, generally referenced520, comprises an aperture tunneling well with punctual drawn linkbetween the two wells, and with gate 526 and contacts 528 placedthereover to generate two qdots 522, 524.

A diagram illustrating a second example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AC. The structure,generally referenced 530, comprises the physical realization of thestructure of FIG. 9AB with a narrow link channel formed between the twowells using a suitable technique such as optical proximity correctionchannel, and with gate 536 and contacts 538 placed thereover to generatetwo qdots 532, 534.

Note that it is not mandatory that the two wide wells have a punctualcontact in order to obtain a narrow link channel between them. In somecases, it is sufficient that they are placed in very close proximity,and optical proximity correction results in a link channel in thephysically realized shapes.

A diagram illustrating a third example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AD. The structure,generally referenced 540, comprises an aperture tunneling well withoutcontact between the two wells but in very close proximity, and with gate546 and contacts 548 placed thereover to generate two qdots 542, 544.

A diagram illustrating a fourth example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AE. The structure,generally referenced 550, comprises the physical realization of thestructure of FIG. 9AD with a narrow link channel formed between the twowells using a suitable technique such as optical proximity correctionchannel, and with gate 556 and contacts 558 placed thereover to generatetwo qdots 552, 554.

Note that the narrow channel link of the induced depletion regionseparating the two wider quantum wells can have any given orientation,e.g., horizontal, vertical, or any arbitrary angle. In addition, thecontrol gate may overlap the narrow channel link, or it may also overlapthe edges of the adjacent wider quantum wells. The former is preferredsince it results in a smaller parasitic capacitance and thus a largerCoulomb blockade voltage.

A diagram illustrating a fifth example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AF. The structure,generally referenced 560, comprises an aperture tunneling well with anangled drawn link between the two wells and gate overlap only on thelink channel 569, and with gate 566 and gate contacts 568 placedthereover to generate two qdots 562, 564.

A diagram illustrating a sixth example quantum structure with cornerabutting rectangular shaped wells is shown in FIG. 9AG. The structure,generally referenced 570, comprises an aperture tunneling well with anangled drawn link between the two wells and gate overlap on both thelink channel 579 and the wells themselves, and with gate 576 andcontacts 578 placed thereover to generate two qdots 572, 574.

It is appreciated that the fabrication of the quantum structure examplesdescribed supra is not limited to one process only but can be fabricatedusing any number of semiconductor processes. Examples include (1) planarsemiconductor processes with depletion tunneling, (2) planarsemiconductor processes with oxide tunneling, (3) 3D (FinFET)semiconductor processes with depletion tunneling, and (4) 3D (FinFET)semiconductor processes with oxide tunneling.

Single Particle Operation

It is important to note that to achieve quantum operation: (1) carriers(electrons or holes) need to be isolated, (2) information needs to beconveyed to the electrons in either their position or spin (or both),and (3) multiple carriers are allowed to interact (i.e. entangle) beforea reading (referred to as detection) of the quantum state is performed.

First, single carriers are separated out of the collectivities ofcarriers that usually exist in semiconductor layers in classic circuits.A semiconductor layer is formed of a network of semiconductor atoms thatcontribute carriers to a collective of carriers described by an energyband. Dopants are introduced into semiconductor layers in order toenhance the concentration of a given type of carriers. Donor dopantsincrease the number of electrons yielding an N-type semiconductor layerwhile acceptor dopants increase the number of holes yielding a P-typesemiconductor layer.

When the semiconductor contains a very large number of carriers actingas a collectivity, adding one carrier to the collectivity or subtractingone carrier from the collectivity does not change the potential. Toachieve a single carrier (e.g., single electron) behavior it is bestthat the considered particle does not have a large collectivity ofcarriers that it can interact with.

An undoped semiconductor or undoped semiconductor layer has a very lowconcentration of carriers. It still contains a large number of carrierscompared with the single carrier that is needed for quantum operations.Doped semiconductor layers have even more carriers and thus are lessattractive for single electron operation.

To achieve single carrier behavior in semiconductor layers it ispreferable to first deplete them of carriers before performing thesingle electron operations. It is relatively easy to deplete anintrinsic (i.e. undoped) semiconductor and even a low dopedsemiconductor. Depleting a higher doped semiconductor layer is harderand requires much larger potentials to achieve depletion. Furthermore,it is easier to deplete a thin layer of semiconductor than it is todeplete a thick layer of semiconductor. Thus, for building semiconductorquantum structures based on single electron behavior, an SOI processhaving a thin top active layer and an oxide layer to isolate the toplayer from the substrate is preferred.

In such processes, the body of the devices is relatively easy to fullydeplete. In most cases even the work function between the gate and thethin active layer is enough to generate a full depletion of the thinlayer. In other cases a certain gate voltage may be needed to fullydeplete the body of the device. In fully depleted processes, the thinsemiconductor layer is depleted of free carriers due to the presence ofone or more control gates on top.

Once the semiconductor layer is fully depleted, there are no other freecarriers that can interact with the quantum particle(s) and quantumeffects can come forth. In a fully depleted well (which may haveinitially been undoped or low doped), the potential on the control gateson top determines the its profile. Such potential profile may, forexample, have valleys and peaks. The valleys is where a carrier may belikely located and the peaks constitute tunneling barriers that mayprevent the particle(s) from moving from one position to another.

In such a fully depleted semiconductor layer (CAD drawn layer may beundoped or low doped) a single carrier (e.g., electron) may be injectedusing an interface device. The particle may be trapped in a givenlocation in the depleted well where the potential has a valley boundedon both ends by tunnel barriers. By appropriately changing the controlsignals on the gate, the potential in the well and the heights of thebarriers can be modified and thus the single particle may move from onelocation to another in the fully depleted well. This is the basis of theoperation of the charge/position quantum qubit.

Classic FET transistors, on the other hand, have higher doped regionsfor the source and drain. In bulk processes, the higher doped source anddrain regions are formed directly in the body well by implanting ordiffusing dopants. In fully depleted SOI processes where a thinsemiconductor film is deposited on top of the BOX oxide that providesisolation from the substrate, the source and drain regions are realizedby depositing another layer of high doped semiconductor on top of theundoped thin layer.

The interface devices have on one side of the gate a higher doped layerthat behaves classically and carriers that behave collectively, whileunder the gate and on the opposite side thereof is the original undopedlayer which is fully depleted. The gate terminal determines the heightof the tunnel barrier and may allow a single particle to be injected inthe fully depleted well. The particle will be localized in the fullydepleted well in a region where a valley of the potential is present.From this point on a quantum operation may be performed on the singlecarrier that was separated from the classic collectivity of carrierspresent on the classic well of the device.

Half Classic/Half Quantum Interface Device and Example Structures

The interface device disclosed herein is operative to provide a linkbetween classic electronic circuits and quantum circuits. A well is afairly isolated semiconductor layer that can be part of a device. Aclassic well is contacted with metal layers to other devices and usuallyhas a large number of free carriers that behave in a collective way,sometimes denoted as a “sea of electrons.” A quantum well, however, isnot connected to classic devices that may have a sea of electrons. Thequantum well may or may not have contacts and metal on top, but suchmetal is left floating. A quantum well holds one free carrier at a timeor at most a few carriers that have single carrier behavior.

The ability to inject one single carrier at a time is needed to operatea quantum structure. The charge of a carrier (i.e. electron or hole) is1.6×10⁻¹⁹ Coulomb. The charge is the integral of the current over agiven time interval. Classic devices operate with current that areusually in the 0.1 uA and higher level. If a 0.1 uA current is used toinject a single electron, the pulse width of the current needs to be1.6'10⁻¹² sec. A pulse in the 1 ps range could require clock frequenciesin the THz range if implemented straightforwardly with clocks, which arenot available in current integrated semiconductor processes.Furthermore, the dependence of the transistor current on the appliedvoltage is relatively moderate, e.g., quadratic or even linear. Thus, inorder to stop the current flow a large voltage difference is required.Such a voltage is much larger than what a typical Coulomb blockadevoltage is in currently available semiconductor processes.

To stop the flow of current with a Coulomb blockade voltage, the currentdependence on the voltage needs to be very steep, e.g., exponential.Such current to voltage dependencies are achieved in deep subthresholdregimes when a tunneling current is present in the device.

To inject a single electron with a pulse in the 100 ps range requires acurrent of 1 nA. Such a current puts the small nanometer devices in deepsubthreshold mode of operation. In this regime a tunnel current withexponential voltage dependence is established between the twowells/sides of the device.

In classic electronic circuits operating at room temperature if theinterface device generates a 1 nA current multiple carriers (i.e.electrons) will be transferred to the second well provided that a closedpath is established for the device current. If the second well isconnected electrically, there is no force that will oppose the flow ofadditional carriers in the second well. When the second well is leftfloating, a different behavior is ensured.

To achieve quantum operation the devices are cooled down to deepcryogenic temperatures such that the thermal noise or thermal agitationof the carriers is minimal. Also, the quantum devices need to usedimensions in the nanometer range, such that the capacitance of thestructure is in the 100 aF range. In such cases the Coulomb blockadevoltage becomes multi-millivolt level. This is needed since thetransport of a single carrier from the classic well to the quantum wellrequires a change of potential (Coulomb blockade) large enough that thetunnel current is reduced significantly and no further carrier willtunnel to the quantum well. The dependence of the tunnel current on thepotential difference between the gate and the well is exponential.Therefore, voltage changes of a few to tens of millivolts can readilystop the further tunneling of subsequent particles.

In a half-classic, half-quantum interface device the Coulomb blockadegenerated by the tunneling of a single carrier to the quantum wellprevents other carriers from tunneling. In order to establish theinitial tunneling current from the classic well to the quantum well, apotential difference is established between the well and the controlgate. In one embodiment, the interface device is realized by placing acontrol gate over a continuous well. The potential of the gate which isdirectly driven or has its potential imposed for example by a capacitordivider such that a depletion region is established under the controlgate thereby separating the well into two sections: one classic and onequantum. The classic well is connected to other classic devices usingmetal layers. In order to control the device with the gate signal, thepotential of the classic well needs to be set at a certain referencevalue. This is done with a classic FET transistor that resets thepotential of the classic well during a rest time period.

With the classic well sitting at a V_(classic_ref) potential, thepotential of the gate is changed by a control signal such that asubthreshold tunnel current is generated in the interface device. Thesign of the gate potential depends on the doping type, the level of thewell, and the material of the gate and oxide which in turn set the workfunction difference. In the case of a P-type well the gate voltage needsto be more positive than the classic well potential, assuming a zerowork function difference.

In this manner a pulse signal applied at the gate of the interfacedevice determines the tunneling of precisely one particle (e.g.,electron) from the classic to the quantum well. The pulse duration doesnot need to be very precise. It just needs to be longer than what isneeded to securely tunnel a single particle. No further particle will betunneled, even though the pulse may be longer because of the Coulombblockade voltage that will exponentially reduce the tunnel currentlevel.

Once a single carrier (e.g., electron or hole) is injected into thequantum well, a pure quantum operation can be performed. Usingadditional control gates on top of the continuous well which furtherisolates quantum dots in the structure, the carrier may be transportedin a discrete fashion from one qdot to another. If appropriate controlsignal pulse widths are applied, the particle (actually, itswavefunction) may be split between two or more qdots. In one embodiment,a quantum structure can have a plurality of wells with a plurality ofqdots. If the wells are brought in close proximity at least in a certainlocation, interaction (i.e. entanglement) between quantum particles canoccur.

In one embodiment, a quantum structure comprises one or morehalf-classic, half-quantum interface devices. Each interface deviceinjects a single carrier or multiple carriers but at different timeinstants, with one carrier at a given time.

The gate-to-classic well potential difference needed to realize thetunneling of the single carrier varies with process and location of thedevice. It also varies with the temperature of the structure. Tomitigate such variability, the gate control signal has adjustabilitybuilt-in such as via a digital to analog converter (DAC) and acalibration engine to set the appropriate voltage level for eachindividual injection device (i.e. half-classic, half-quantum interfacedevice).

A diagram illustrating a first example interface device of the presentinvention in more detail is shown in FIG. 10A. The device, generallyreferenced 802, comprises a conventionally doped diffusion region 812and one or more metal contacts 814, gate 806 and gate contacts 804, anda non-doped (intrinsic or no diffusion) or very low doped (n−−, p−−)region 820 having no or low n- or p-doping, diffusion, and no contactsnor metal. The doped diffusion region 812 is either low doped (n−, p−),medium doped (n, p), high doped (n+, p+), or highly doped (n++, p++).The doped semiconductor side 812 of the gate 806 connects to classicalsemiconductor electronic circuity 816, which can comprise a particle(e.g., electron) injector controller, a gate imposer controller, and aparticle detector in addition to various other control, detection andprocessing functionalities (see FIG. 2). The gate 806 can also connectto the circuitry 816 (not shown). The non-doped side 820 of the gate 806connects to quantum semiconductor circuits 818. Thus, half the devicecontains classic carriers in energy bands and the other half containsquantum carriers in discrete energy levels. The transport of carriersfrom the classic side to the quantum side of the device is realizedthrough tunneling through highlighted region 808. An appropriatepotential applied to the gate is operative to connect a particle fromthe quantum side to the classic side of the interface device. This way,the quantum particle can electrically join the potential sea ofcarriers. Note that the labels ‘quantum side’ and ‘classic side’ are forconvenience sake since at the fundamental level there is nothinginherently quantum or classic with the two sides of the gate.

In operation, the interface device 802 functions to provide an interfacefrom conventional electronic circuitry located on (or off) theintegrated circuit to quantum circuits and vice versa. In particular,the interface device is operative to separate a single quantum particle824, e.g., electron, etc., from a plurality of particles 822. A singlequantum particle is allowed to tunnel (indicated by arrow 810) throughthe depletion region 808 in an injector mode of operation. Anappropriate gate control signal is applied to the gate 806 to establishthe energy barrier and to control the tunneling through the depletionregion. Note that an appropriate potential might need to be set on dopedregion 812 prior to this operation. Thus, the interface device functionsas an injector tunneling device that allows the tunneling of a singlequantum particle, or alternatively a controllable number of particles.When the gate potential is carefully lowered, a single quantum particle(e.g., electron) is allowed to tunnel from the left to the right side ofthe device.

In addition, in one embodiment, the logical flow of electrons can beprovisioned to function in the opposite direction whereby the interfacedevice is part of a circuit that senses and detects the presence of asingle particle. In this case, the interface device can serve as thesensor which is coupled to additional classical circuitry (not shown) todetect the presence of single particles. In particular, if thecapacitance on the classic side of the device is sufficiently lowenough, the presence of a single particle (e.g., electron) on thequantum side of the device can be sensed or detected on the classicalside of the device using conventional electronic circuitry, such as 816.This is achieved by detecting the rise in voltage magnitude on theclassical side caused by the presence of the single particle on thequantum side upon lowering the barrier of the gate 806. Thus, theinterface device is capable of operating bidirectionally as both aninjector of a single particle and a detector of a single particle.

Note that in operation, on the classic side of the interface device, thequantum particles, e.g., electrons, are in energy bands, i.e. conductionband and valence band, which enables current flow in classicsemiconductor devices. On quantum side of the interface device, thequantum particle is in discrete energy levels with one or two electrons(spin up and down) in each level.

A diagram illustrating a second example interface device of the presentinvention is shown in FIG. 10B. It is appreciated that the interfacedevice can have many shapes depending on the particular implementationof the invention. In this example, the interface device, generallyreferenced 830, has an ‘L’ shape and comprises a conventionally low,medium, high, or highly doped region 838 with one or more metal contacts836, gate 834 and gate contacts 832, and a smaller non-doped (intrinsic)or very low doped region 839 without n+ or p+ doping, contacts, ormetal. Note that the ‘L’ shape helps provide shifting on the y-axis andthus increases the distance from other structures.

A diagram illustrating a third example interface device of the presentinvention is shown in FIG. 10C. In this example, the interface device,generally referenced 840, has a diagonal shape and comprises aconventionally low, medium, high, or highly doped region 848 with one ormore metal contacts 846, gate 844 and gate contacts 842, and a smallernon-doped (intrinsic) or very low doped region 849 with n−− or p−−doping.

A diagram illustrating a cross section of a first example semiconductorquantum structure and conventional FET is shown in FIG. 11. Thestructure, generally referenced 850, comprises a conventional classicFET on the left, a fully quantum device on the right, and a halfclassic/half quantum interface device in the middle. All three devicesare fabricated on substrate 852 and oxide layer 854. It is appreciatedthat other types of substrates are possible as well.

The fully depleted quantum device on the right comprises two qdots inwell 879 separated by metal or polysilicon gate 864 and oxide layers870, 872 over depletion region 868. The gate modulates tunneling (arrow869) between the two qdots as described in detail supra. Note that thetwo qdots on either side of gate 864 have no diffusion, contacts ormetal.

The fully quantum device on the right comprises two qdots in well 879separated by metal or polysilicon gate 864 and oxide layers 870, 872over depletion region 868. The gate modulates tunneling (arrow 869)between the two qdots as described in detail supra. Note that the twoqdots on either side of gate 864 have no diffusion, contacts or metal.

The half classic/half quantum interface device in the middle comprisesmetal or polysilicon gate 862 and oxide layers 870, 872 over depletionregion 866. The gate modulates tunneling (arrow 867) to allow a singlequantum particle to tunnel between doped region 878, 874 on the leftside of the gate 862 and the qdot on the right side of the gate. Thehalf classic/half quantum interface structure thus functions to providean interface mechanism between classic electronic circuitry on the leftand quantum circuitry on the right.

A diagram illustrating a cross section of a second example semiconductorquantum structure and conventional FET is shown in FIG. 12. Thestructure, generally referenced 880, comprises a conventional (i.e.classic) FET on the left, a fully quantum device on the right, and ahalf classic/half quantum interface device in the middle. All threedevices are fabricated on substrate 892 and oxide layer 894.

The classic FET on the left comprises source, drain, and gate includingdoped well 882, 918 connected to contact 916 and metal 896 structureslocated on either side of metal or polysilicon gate 898 built over oxidelayers 910, 912. In classic FET operation, mobile carriers travel fromsource to drain through inversion channel 914 in accordance with thepotential applied to the gate, source and drain terminals.

The fully quantum device on the right comprises two qdots in well 908separated by metal or polysilicon gate 900 and oxide layers 902, 904over depletion region 887. The gate modulates the tunneling (arrow 886)between the two qdots as described in detail supra. Note that the twoqdots on either side of gate 900 have no diffusion, contacts or metal.

The half classic/half quantum interface device in the middle comprisesmetal or polysilicon gate 899 and oxide layers 902, 904 over depletionregion 885. The gate modulates the tunneling (arrow 884) between theregion on the left of the gate to the region on the right. In thisembodiment of the interface device, the doped region 918, 906 of drainof the classic FET is moved closer to the gate 898 and a non-diffusionregion is inserted on the left side of the gate 899 in order to reduceparasitic capacitance. The half classic/half quantum interface devicefunctions to provide an interface mechanism between classic electroniccircuitry on the left and quantum circuitry on the right.

A diagram illustrating a cross section of a third example semiconductorquantum structure and conventional FET is shown in FIG. 13. Thestructure, generally referenced 920, comprises a conventional (i.e.classic) FET on the left, a fully quantum device on the right, and ahalf classic/half quantum interface device (i.e. interface device) inthe middle. All three devices are fabricated on substrate 922 and oxidelayer 924.

The classic FET on the left comprises source, drain, and gate includingdoped well 938, 936, 954 connected to contact 928 and metal 926structures located on either side of metal or polysilicon gate 930 builtover oxide layers 942, 944. In classic FET operation, mobile carrierstravel from source to drain through inversion channel 940 in accordancewith the potential applied to the gate, source and drain terminals.

The fully quantum device on the right comprises two qdots in well 956separated by metal or polysilicon gate 934 and oxide layers 946, 948over depletion region 962. The gate modulates tunneling (arrow 964)between the two qdots as described in detail supra. Note that the twoqdots 950, 952 on either side of gate 934 have diffusion but no contactsor metal.

The half classic/half quantum interface device in the middle comprisesmetal or polysilicon gate 932 and oxide layers 946, 948 over depletionregion 960. The gate modulates tunneling (arrow 958) between thediffusion region 936, 954 on the left side of the gate 932 and well 956with diffusion 958 on the right side of the gate. The half classic/halfquantum interface device functions to provide an interface mechanismbetween classic electronic circuitry on the left and quantum circuitryon the right. Note that in one embodiment, similar structures can bebuilt using bulk processes with no oxide layer under the quantumstructure but with a depletion region instead.

As described supra, the quantum processor of the present inventioncomprises a mix of structures including quantum structures,conventional/classic FET structures, and interface devices comprisinghalf classic and half quantum operation which are used to moveinformation from the conventional FET (i.e. non-quantum) domain to thefull quantum domain.

A diagram illustrating an example quantum structure with interfacedevices is shown in FIG. 14. The example structure, generally referenced670, comprises a middle full quantum structure (dashed circle 683)having gate 689 sandwiched by a left side interface device structure(dashed circle 681) with gate 674 and a right side interface devicestructure (dashed circle 685) with gate 676. The interface devices 681,685 comprise a conventional FET (darkened areas 684, 687) on one side oftheir gate and quantum device on the other side.

The structure 670 comprises two qdots and utilizes well-to-welltunneling through local depleted region. An interface device is locatedat each end for interfacing with conventional electronic circuits. Thepotential on the control gate can be applied either with a directvoltage drive network or via a floating impedance division. The well isrealized with two rectangular wells having an overlap to create thenarrow tunneling channel 671.

A diagram illustrating a first example multiple qdot quantum structurewith interface devices on either end thereof is shown in FIG. 15A. Thehigher complexity semiconductor quantum structure, generally referenced690, comprises a continuous well with a plurality of imposing controlgates 696 and gate contacts 692 that separate it into a plurality ofqdots 698. In this example, the well comprises a plurality ofoverlapping squares connected at their corners to create a narrow tunnelpath 699. Located at either ends of the well are interface devices 694that allow the connection of the reset, injection and detectioncircuits. The imposer gates 696 receive pulsed control signals thatdetermine the specified quantum operation.

A diagram illustrating a CAD layout of an example quantum structure isshown in FIG. 15B. The layout, generally referenced 700, comprises acontinuous well with a plurality of control gates 706 and gate contacts704 that form a plurality of qdots 702. In this example, the wellcomprises a plurality of abutting squares connected at their edges tocreate a tunnel path. Located at either ends of the well are interfacedevices 708 with contacts 709 that allow the connection of the reset,injection and detection circuits (not shown). Note that these threecircuits can be all electrically connected to the same node, forexample, 812 in FIG. 10A.

A diagram illustrating a cross section of the quantum structure of FIG.15A is shown in FIG. 16. The quantum structure has multiple qdots withinterface devices at both ends of the well. The single continuouslydrawn well is separated into a plurality of qdots by the local depletionregions induced by a plurality of control gates. The cross section 710comprises a substrate 712 and oxide layer 714 on which are fabricatedseven qdots 722 comprising six control gates 722 each including oxidelayers 728, 730, and polysilicon or metal layer 726, two interfacedevices 720 each including n or p doped regions 718, 716, contact 711,and metal layer 713, and gate 732.

To illustrate the operation of the quantum structure of the presentinvention, a series of diagrams are presented that show the stepsinvolved in an example quantum operation starting with a single quantumparticle where the local depletion region is under control of the gate.

A diagram illustrating the aperture tunnel barrier for a two quantum dotstructure is shown in FIG. 17A. The local depletion region under thecontrol gate divides the structure into two qdots, namely a left qdotstorage 741 and a right qdot storage 743. The tunnel barrier imposed bythe local depletion region is represented by trace 740. In this phase,the depletion region is wide and the tunnel barrier is high (referenced742) and the particle 746 cannot tunnel to the right qdot storage and istrapped in the left qdot storage.

A diagram illustrating a first example change in the aperture tunnelbarrier for the two quantum dot structure is shown in FIG. 17B. Thetunnel barrier imposed by the local depletion region is represented bytrace 744. In this phase, an appropriate potential is applied to thecontrol gate to cause the depletion region to narrow thus lowering thetunnel barrier (referenced 745). This permits the particle 748 to travelto the right qdot storage and the particle is in the left and rightqdots at the same time.

A diagram illustrating a second example change in the aperture tunnelbarrier for the two quantum dot structure is shown in FIG. 17C. Thetunnel barrier imposed by the local depletion region is represented bytrace 750. In this phase, the potential applied to the control gate isadjusted to cause the depletion region to widen again thus raising thetunnel barrier (referenced 752). This effectively traps the two splitparticles 747, 748 (i.e. the wavefunction of the particle is split) andprevents them from traveling from one qdot to the other through thetunnel barrier. In quantum fashion, the charge carrier is split betweenthe two qdots. When performing detection, however, the carrier will onlybe on one side with a corresponding probability.

Thus far only electric control of semiconductor quantum structures hasbeen presented wherein the spin of the quantum particle is ignored. Analternative manner of controlling the semiconductor quantum structure isto control/select the spin of the quantum particle using a magneticfield from an inductor/coil or a resonator. A property of particles isthat they tend to align their spins to any external relatively strongmagnetic field. A diagram illustrating an example quantum structuresurrounded by a spin control magnetic coil is shown in FIG. 18.

The structure, generally referenced 760, comprises a resonator 763 orone or more turns of a coil 762 surrounding a continuous well dividedinto two qdots 764 by control gate 766 and connected by tunnel path 768.Along with the electrical control of the imposing gate, this structurealso uses the magnetic field generated either by (1) an inductor 762 or(2) a resonator 763 that surrounds the entire quantum structure toselect the spin of the particle. Note that both are shown in the figurebut in practice typically only one is implemented. Note also that bothstatic and ac magnetic fields can be generated and used. In addition,the inductor may overlap only a local area including one or severalquantum structures or it can overlap the global area where the quantumcore is implemented. In this manner, local magnetic control or globalmagnetic control can be implemented.

As described supra, the quantum computer operating environment employscooling at cryogenic temperatures. In addition, electric and magneticfield shielding is provided. The cryostats used typically compriserelatively large metal structures that act as good shields. In oneembodiment, the metal cavity of the cryostat creates a high qualityresonator that generates a magnetic field to control the semiconductorquantum structures at its interior.

A diagram illustrating a second example multiple qdot quantum structureis shown in FIG. 19. The structure, generally referenced, 770, comprisesa blended continuous well path 772 overlapped by a plurality of controlgates 776 with contacts 774 (three in this example). Here the width ofthe vertical segments of the control gates and the vertical andhorizontal segments of the well are the same, i.e. a “boomerang”structure in which the width of the wider well regions is made equal tothe width of the narrow channel links. Such a structure results in amore compact realization of the quantum structure. Note that the regionsbetween control gates form the quantum dots, while the regions under thecontrol gates realize the induced depletion regions through whichtunneling occurs. It is appreciated that any number of qdot structurescan be realized depending on the number of control gates implemented.Note that in one embodiment, such structures can be implemented usingeither planar or 3D semiconductor processes.

A diagram illustrating a third example multiple qdot quantum structureis shown in FIG. 20. In an alternative embodiment, the semiconductorstructure comprises a bended well path overlapped by gates usinghorizontal and inclined well segments. Note that vertical segments alsopossible. In particular, the structure, generally referenced, 780,comprises a blended continuous well path 782 overlapped by a pluralityof control gates 786 with contacts 784 (three in this example) usinghorizontal and inclined well segments. Here too the width of thevertical segments of the control gates and the vertical and horizontalsegments of the well are the same, i.e. a “boomerang” structure in whichthe width of the wider well regions is made equal to the width of thenarrow channel links. Such a structure results in a more compactrealization of the quantum structure. Note that the regions betweencontrol gates form the quantum dots, while the regions under the controlgates realize the induced depletion regions through which tunnelingoccurs. It is appreciated that any number of qdot structures can berealized depending on the number of control gates implemented.

A diagram illustrating a fourth example multiple qdot quantum structureis shown in FIG. 21. In an alternative embodiment, the semiconductorstructure comprises a bended well path overlapped by gates usinghorizontal and rounded well segments. Note that vertical segments alsopossible. In particular, the structure, generally referenced, 790,comprises a blended continuous well path 792 overlapped by a pluralityof control gates 796 with contacts 794 (three in this example) usinghorizontal and rounded well segments. Note that the regions betweencontrol gates form the quantum dots, while the regions under the controlgates realize the induced depletion regions through which tunnelingoccurs. It is appreciated that any number of qdot structures can berealized depending on the number of control gates implemented.

Quantum State Detection

In semiconductor quantum structures and circuits, the qubits (i.e.elementary quantum information units) are encoded by the state ofparticles or carriers inside one or more semiconductor layers. To helpto achieve the single carrier behavior, the semiconductor layers areusually fully depleted. In the case of spin qubits the detectionincludes determining the spin orientation of a given carrier (e.g.,electron or hole), while in the case of charge qubits (i.e. positionqubits) the detection includes determining if the carrier is present ornot in a given qdot.

Classically, a bit can have only two values “0” and “1”. In the quantumdomain, however, a qubit can have a large number of values given by anyconstrained combination of the two base quantum states |0> and |1>. Thisis provided by the superposition character of the quantum states.

When a quantum state is detected, the quantum state is collapsed into abase state which corresponds to a classic state with a given probabilityassociated with it. For example, in the detection of a charge qubit, theoutcome can be either: (1) the carrier is present in the detection qdotwhich corresponds to the base state |1>; or (2) the carrier is notpresent in the detection qdot which corresponds to the base state |0>.To determine the value of a quantum state, a number of successivequantum experiments are performed to get the average presenceprobability of the detected carrier. By computing the number of |0>s and|1>s that are obtained in the detection, the probability of the quantumstate is determined.

For example, consider the Hadamard equal distribution quantum statedenoted by 0.707|0>+0.707|1> where the carrier is split equally into twoqdots of the quantum gate. From the quantum perspective, this means thecarrier is present simultaneously in both qdots. In the classic view,the electron cannot be split and it either is present in a given qdot orit is absent from that qdot. When detecting a Hadamard state multipletimes it is expected to obtain an equal number of collapses to the |0>base state (i.e. the carrier is absent) and to the |1> base state (i.e.the carrier is present) in the detected qdot. If the quantum state has agiven rotation and it has a larger |1> base state component (a|0>+b|1>with b>a) then at detection more collapses to the base state |1> shouldoccur. If in contrast, the quantum state has a rotation towards the |0>base state (a|0>+b|1> with a>b) then more collapses to the base state|0> should occur.

In order to perform detection of a quantum state contained in a quantumdevice, the quantum structure is connected to classic devices. This isachieved using an interface device, described in detail supra. Suchinterface devices are half-quantum and half-classic in their nature orinterpretation. In one embodiment, the detector circuit itself comprisesclassic devices that process charge, current, and voltage. The quantumdevices operate with single carrier (e.g., electron or hole), or a smallcontrollable number thereof, while the interface device extracts asingle carrier from a sea of collective electrons in the classic worldor vice versa injects a single carrier into a classic world sea ofcollective carriers.

In one embodiment, the classic device of the detector is connected at aquantum structure using a floating well, in which the interface devicehas a quantum well on one side and a floating classic well on the other.Since the classic well is set to be floating, the injection of a singlecarrier may result in a noticeable well potential change that can beamplified further.

In another embodiment, the classic device of the detector is connectedat a quantum structure using floating gate detection. In this case, theinterface device is realized by a device having a plurality of gates,one of them being shared with a classic FET detector device. When thecarrier arrives under the floating gate of the interface device itchanges the potential of the gate, which in turn can be measured by theclassic FET of the detector which shares the gate with the interfacedevice.

Floating Well Detection

In floating well detection, the quantum particle is injected from thequantum device (if it happens to be present there) into a classicfloating well that is in turn connected to the input of the classicdetector circuit. An equivalent schematic of the quantum circuit,generally referenced 990, together with its associated interface andclassic circuits is shown in FIG. 22A. A top plan layout view of thecircuit is shown in FIG. 22B and a cross section of the circuit is shownin FIG. 22C. The quantum circuit 990 comprises several layers includingsubstrate 1010, BOX oxide 1008, and undoped fully depleted layer 1006.Doped regions 1020 are fabricated over the fully depleted layer.

In one embodiment, before starting a quantum operation, the entirequantum structure is reset, i.e. the entire quantum well is flushed ofany free carriers. Since the quantum well is fully depleted, there areno carriers in it. A reset operation is performed by one or more classicMreset devices 992 by appropriately controlling the interface quantumgates (Qinterface) 994 and imposer quantum gates (Qimp) 996. The classicMreset device comprises metal contacts 1002 on its terminals realized bydoped semiconductor layers 1020. Considering the SOI semiconductorprocess as an example, the source and drain doped diffusions arefabricated above the undoped fully depleted device body 1006. The Mresetdevice establishes a reference potential for the classic side of theclassic to quantum interface device on the left. During the quantumoperation it is assumed that this potential does not change much due toleakage currents.

In one embodiment, quantum operation begins by initially resetting theclassic well to a reference potential then setting it floating duringthe detection time interval. A single carrier (e.g., electron or hole,if one happens to be present there) is injected from a classic well 1022where a sea of carriers have a collective behavior, into a quantum well1024 where single carrier behavior can occur. An appropriate potentialis applied to the gate 1004 of the Qinterface device 994 to control thetunneling of a single particle 1012 to the quantum side by lowering thetunneling barrier. Once the single particle is injected into the fullydepleted well 1024, it moves according to the potential distributionchange determined by the plurality of quantum imposing gates (Qimp) 996.In one embodiment, the Qimp gates determine the creation of valleys inthe potential distribution that is progressively shifted from left toright and thus determine the movement of the particle 1012. Depending onthe timing and pulse widths of the Qimp signals, a carrier may be splitbetween different locations in the fully depleted well in which two ormore potential valleys may be realized. This is the base of generatingthe superposition quantum states (a|0>+b|1>).

At the opposite end of the well, a second interface device 998 providesthe interface in the other direction from the quantum well 1026 to theclassic well 1014. In one embodiment, the classic well is left floating(no dc path to ground) such that the potential injection or transfer (byvirtue of the connecting transistor 998) of a single carrier cangenerate a measurable change in potential that is further processed bythe detector classic circuit 1000. Since the particle is injected (ortransferred) from the quantum well into a classic well, the quantumstate collapses. This detection is destructive since the quantum stateis destroyed during the measurement process. It is destroyedspecifically during the instance the particle sees a low resistancepath, i.e. is connected, to the sea of carriers on the classic side. Itis noted that such destructive detection can be performed only once perquantum operation. Furthermore, it is noted that another reset devicesimilar to 992 can be connected to the same node 1014 as that connectedto the detector 1000. Likewise another detector similar to 1000 can beconnected to the reset device 992 (node 1003). These two types ofcircuits operate in a time shared manner in which the active time slotsallocated to them can be different. Their high resistance during theinactive time slots ensures no conflicts.

The floating classic well 1014 is connected to the gate 1016 of adetection device 1000. The floating well and the gate 1016 of thedetector Mdetector have a certain total capacitance. The voltage changein the signal at the gate 1016 of Mdetector is given by ΔV=e/C where eis the carrier charge 1.6×10⁻¹⁹ Coulomb and C is the total capacitanceof the floating well (1014 and possible 1026) and gate. In oneembodiment, the charge to voltage conversion is followed by classicvoltage or transconductance amplifiers depending on the voltage mode orcurrent mode operation of the classic detector circuit 1000. Note thatthe entire single carrier (e.g., electron) injection, quantumprocessing/imposing and detection is short in comparison with thedecoherence time of the particle in the given semiconductor structure.

Note that other classic analog, mixed signal or digital circuits arepreferably kept an exclusion distance away from the quantum structure990 in order to avoid undesired parasitic interaction with the quantumparticle(s) that could lead to quantum decoherence.

Floating Gate Detection

The second option for the detection of the quantum state is to use afloating gate. In this case the classic device of the detector Mdetectoris connected to the same floating gate that goes over the quantum well.An equivalent schematic of the quantum circuit, generally referenced1030, together with its associated interface and classic circuits isshown in FIG. 23A. A top plan layout view of the circuit is shown inFIG. 23B and a cross section of the circuit is shown in FIG. 23C. Thequantum circuit 1030 comprises several layers including substrate 1050,BOX oxide 1048, and undoped fully depleted layer 1046. Doped regions1058 are fabricated over the fully depleted layer.

Similar to the floating well detection circuit 990 described supra, thequantum procedure starts with the reset of the structure 1030 using oneor more classic Mreset devices 1032 along with appropriate control ofthe interface quantum gates (Qinterface) 1034 and imposer quantum gates(Qimp) 1036 such that all free carriers in the quantum structure areflushed out. The classic to quantum Qinterface device 1034, operative toinject a single carrier 1052 into the quantum structure, has ahalf-classic and half-quantum operation. It comprises a doped and metalcontacted classic well 1054 on the left side of its gate 1044 and afloating quantum well 1056 on the other side. In one embodiment, theconnection between the Mreset and Qinterface devices on the classic sideis realized with contacts and metal layers 1055. Note that the Mresetand Qinterface devices may share the same active layer or may be done inseparate active layers.

The quantum imposer (Qimp) devices 1036 determine the specific quantumcomputation performed. There is at least one Qimp quantum control gate.Alternatively, the circuit may comprise any number of Qimp devices aslarge as feasible in the actual implementation using a givensemiconductor process.

The last three gates over the quantum well on the right side of thecircuit 1030 form a quantum to classic Qinterface device 1038, 1064,1062. Note that alternatively, the Qinterface device may be located inthe middle of a quantum well. One of the three gates (1060) is thefloating gate which connects to the Mdetector classic detector device1040. In one embodiment, the carrier is moved under the floating gate bycontrolling the potential distribution with the two adjacent gates 1059,1061. The presence of the quantum carrier under the floating gate causesa change of the potential of the quantum gate which is sensed by theMdetector detector device 1040 and amplified further.

After the first measurement is performed, the quantum carrier can bemoved away from under the floating gate 1060 of the interface device.The floating gate initial potential is set during the reset time to alevel that allows the proper operation of the Mdetector classic detectordevice. Such potential may be reset for example with a second classicMreset device (not shown) connected to the gate of the Mdetector device.

An example potential diagram for the floating gate detection circuit isshown in FIG. 24. The last quantum imposer gate Qimp 1076 together withthe three gates 1077, 1078, 1079 of the quantum to classic interfacedevice (Qinterface) 1070 are shown. In this example, two of the threegates (left gate 1077 and right gate 1079) are controlled and notfloating while only the middle gate 1078 is floating. The middlefloating gate 1078 is connected to the detector circuit 1040 (FIG. 23A).It is appreciated that the Qinterface device may comprise more or lessthan three gates. For example, the detection can be performed using onlytwo interface device gates, i.e. one floating and one controlled.

In operation, the particle is moved one or more times under the floatinggate to perform detection (i.e. nondestructive measurement). Multiplemeasurements are performed under the detection gate for the same quantumexperiment. A measurement is made each time the particle moves under thefloating gate 1078. Note that the movement is speculative in naturesince it is not known a priori whether there is a particle present ornot as this is what is being measured. If no particle is detected, thenof course no movement actually takes place. Potential diagram (A) showsthe quantum particle (e.g., carrier, electron, hole, etc.) 1072 stuck inthe last quantum dot by the last Qimp control quantum gate 1076. Bycontrolling the left 1077 and right 1079 interface device gates thepotential in the fully depleted well 1046 underneath them can bemodified such that a wide valley 1080 is realized which extends underthe floating gate in the middle of the quantum to classic interfacedevice, as shown in potential diagram (B). In this case, the particleextends in the entire area allowed by the potential valley 1080. In thenext step, the control gates modify the potential distribution so thatthe potential valley extends only under the floating gate 1078, as shownin potential diagram (C). Having the particle located directly under thefloating gate generates a change in potential of the floating gate whichcan be measured and amplified by the Mdetector circuit 1040 (FIG. 23A)using one or multiple classic FET devices.

Lowering the potential of the left gate 1077 while raising the potentialof the right gate 1079 extends the valley as shown in potential diagram(D). In potential diagram (E), the valley is restricted and the particlemoves to the right away from the floating gate in potential diagram (F),the interface device gates are configured to widen the potential valleythat extends under both the floating gate and the right interface gate1079. The carrier again will occupy all the space of the valley. In thenext step shown in potential diagram (G), the control gates of theinterface device are configured to change the potential such that thecarrier moves under the floating gate where a new measurement can beperformed. In such case the potential of the floating gate will changein an opposite direction.

In potential diagram (H), the control gates are configured to widen thepotential valley to include the area under the floating gate and inpotential diagram (I), the potential valley is restricted again.

Note that an advantage of the floating gate detection mechanism is thatit is not destructive and the carrier's wavefunction does not collapsein the detection process. This allows the detection of the quantumparticle multiple times. Therefore, instead of performing the entirequantum experiment multiple times, the quantum experiment is performedonce but the results are measured multiple times. This provides for afaster total quantum cycle and helps to increase the fidelity of thequantum operation.

In another embodiment, the floating gate detection may be followed by afloating well detection which finally collapses the quantum state. Byusing both methods of detection, a more sophisticated detection schemecan be built with lower error rate. By looking at the correlationbetween the two types of detection, built-in detection error correctioncan be realized.

3D Semiconductor Quantum Structures

The present invention provides a semiconductor quantum structure thatuses a 3D semiconductor process with very thin semiconductor fins havingmuch smaller parasitic capacitance to the gate. This results in higherCoulomb blockade voltages and thus quantum circuits that are easier tocontrol with classic electronic circuits with more noise floor margin.Two semiconductor islands are isolated in a continuously drawn fin usingan overlapping control gate that induces a local depletion region in thefin. The tunneling between one island in the fin to the other iscontrolled by the control gate that imposes the potential on the fin. Bymodulating the potential applied to the control gate, a controlledfin-to-fin tunneling through the local depletion region is achieved,realizing the function of a position/charge qubit. More complexstructures with higher number of qdots per continuous fin and largernumber of fins can be constructed. 3D semiconductor processes can beused to build such fin-to-fin tunneling quantum structures. Hybrid 3Dand planar structures can be built as well. By combining a number ofsuch elementary quantum structures a quantum computing machine isrealized.

A diagram illustrating an example 3D semiconductor quantum structureusing fin to fin tunneling through local depletion region is shown inFIG. 25. The quantum structure, generally referenced 1840, comprises acontinuously drawn fin 1846, overlapping control gate 1843, two isolatedsemiconductor well and fin structures realize qdots #1 and #2 1842,local depletion region 1848, tunneling path 1841, and particle, e.g.,electron or hole, 1844. A diagram illustrating a three dimensional viewof an example 3D semiconductor quantum structure with fin to fintunneling under control of a control gate is shown in FIG. 26. Thequantum structure, generally referenced 1850, comprises fins withportions 1851, 1853, overlapping control gate 1854, substrate 1855, andlocal depletion region 1852. Note that the well may be omitted and theqdot realized by the semiconductor fin area only.

With reference to FIGS. 25 and 26, the control gate layer overlaps thefin on three sides and creates a local depleted region which isolatesthe two sides when the potential barrier is high. Note that overlappingthe fin provides better control over the structure. A thin oxide layerseparates the semiconductor fin from the control gate. When the controlterminal lowers the potential barrier, tunneling can occur from one sideof the fin to the other side. The tunneling is controlled by the controlterminal that imposes the potential in the semiconductor fin. If thetunnel barrier is high, the quantum particle is locked in its priorstate. When the potential on the control terminal lowers the barrier,the quantum particle can tunnel from one qdot to the other. Depending onthe pulse width of the control signal, the quantum particle completelyor partially tunnels. In the latter case, the quantum particle(precisely, its wavefunction) is distributed between the two qdots, i.e.spatial entanglement. Note that in real implementations, the quantumstructure generally has a deformed complex 3D shape where the depletionregion depends on the particular implementation and semiconductorprocess used. The structures shown herein are for illustration purposesonly.

A diagram illustrating a cross section, side view, and top view of anexample 3D two qdot quantum structure using local fin depletiontunneling is shown in FIG. 27A. The quantum structure, generallyreferenced 1860, comprises substrate 1869, optional oxide layer 1861,wells 1862, 1865, fin 1863, gate oxide 1866, and overlapping controlgate 1864. Note that the dotted line indicates the optional oxide layerthat isolates the 3D quantum structure from the substrate. The substratemay comprise standard resistivity, high resistivity, or isolatingsubstrates.

The tunneling through a local depletion region in the quantum structureis induced in a fin by the overlapping control gate. When the barrier ishigh, the local depleted region is wide and virtually no tunnelingcurrent is allowed. When the barrier is lowered, the local depletedregion shrinks in width and a sizeable leakage tunneling currentappears, which allows the particle to move from one qdot to the other.If the particle has not completed the move from one qdot to the other,it will spread (equally or non-equally) between the two qdots to achievespatial particle entanglement.

A diagram illustrating a cross section, side views, and top view of anexample 3D multiple qdot quantum structure using local fin depletiontunneling is shown in FIG. 27B. The quantum structure, generallyreferenced 1870, comprises substrate 1879, optional oxide layer 1871,wells 1872, 1876, fin 1873, gate oxide 1877, and overlapping controlgates 1874, 1875. Note that the dotted line indicates the optional oxidelayer that isolates the 3D quantum structure from the substrate. Thesubstrate may comprise standard resistivity, high resistivity, orisolating substrates. The quantum structure 1870 is useful when quantumtransport is needed, i.e. quantum shift and particle spatialentanglement, and can be realized in bulk 3D semiconductor processes,e.g., FinFET, or in SOI 3D semiconductor processes.

A diagram illustrating two example double V fin-gate-fin structureshaving two wells placed in close proximity allowing quantum particles tointeract is shown in FIG. 28A. The quantum interaction gate, generallyreferenced 1880, comprises two 3D structures comprising a plurality ofqdots 1882, 1888, fins 1884, control gates 1886, and interaction qdots1881.

In this embodiment, the inner two semiconductor wells 1881 come in veryclose proximity thereby allowing a strong interaction between particlesor distributed particles in the two qdots. The distance between otherpairs of qdots is significantly larger and thus the interaction betweencorresponding particles is much smaller, ideally negligible. In thismanner, the double V quantum structure shifts two or more particles intospecific positions for a well controlled interaction and then transportsthem apart. The preparation of the quantum state also happens whenparticles are further away and thus can be done largely independent onefrom the other. This also allows a well-controlled interaction betweenparticles only when they are in specific qdots and when the controlsignals are configured to enable the interaction.

A diagram illustrating an example 3D semiconductor quantum structureusing fin-to-fin tunneling through a local depleted region with a sharedwell between two fin paths providing bifurcation is shown in FIG. 28B.The quantum structure, generally referenced 1890, comprises a pluralityof qdots 1892, namely qdots #1, #2, #3, #4, fins 1896, and control gates1894. The well of qdot #2 1898 overlaps two fins to provide pathbifurcation whereby particles can move between qdots #1 and #4 andbetween qdots #3 and #4.

Note that this quantum structure can realize either a bifurcation of thequantum operation path or a merger of the quantum operation path. Thisstructure is useful in creating more complex quantum structures. Notealso that the control gates overlapping the two fins and separatingqdots #1 and #3 can be separated (as shown) or can be shared (notshown).

A diagram illustrating an example quantum structure with dummy gates andgate cuts that separate control and dummy gates is shown in FIG. 28C.The quantum structure, generally referenced 1900, comprises qdots 1902,namely qdots #1 to #6, fins 1904, control gates 1901, contacts 1903,dummy gates 1906 not used in operation of the circuit, and gate cuts1908. Depending on the actual 3D semiconductor process used, dummy gatesmay be needed but they remain floating with no potential. The gates needto be equally spaced and on the edges of the well. In addition, they mayneed to be cut in order to prevent unwanted interactions. The cuttingmay be done on top of a dummy fin, or alternatively without the fin.Although 12 control gates are shown, only four are active.

A diagram illustrating an example hybrid planar and 3D semiconductorquantum structure using both fin-to-fin and well-to-well tunnelingthrough local depletion region is shown in FIG. 28D. The quantumstructure, generally referenced 1910, comprises 3D qdots 1912, fins withportions 1914, 1913, 3D control gate 1918, planar qdots 1911, and planarcontrol gate 1916. This hybrid embodiment uses both 3D and planartunneling structures which is possible in a 3D semiconductor process.The inner quantum structure is planar with two overlapping wells (i.e.qdots) and uses well-to-well tunneling through a local depletion region.The outer, i.e. left and right, quantum structures are 3D and usefin-to-fin tunneling through a local depletion region. Note that the twotypes of tunneling have different barrier levels and thus requiredifferent control gate signals.

The present invention also provides a semiconductor quantum structurethat uses a 3D semiconductor process used to fabricate two semiconductorfins and an overlapping imposing control gate that constitutes thetunneling path from one semiconductor qdot to the other. The tunnelingis controlled by the control gate that imposes the potential on thetunneling path. By modulating the potential of the imposer gate, acontrolled fin-gate and gate-fin tunneling through the thin oxide underthe control gate is enabled, realizing the function of a position/chargequbit. More complex structures with higher number of qdots percontinuous well and larger number of wells can be built. Both planar and3D semiconductor processes can be used to build well/fin-to-gate andgate-to-fin/well tunneling quantum structures. Hybrid 3D and planarstructures can be built as well. By combining a number of suchelementary quantum structures a quantum computing machine is realized.

A diagram illustrating an example 3D semiconductor quantum structureusing fin-to-gate tunneling through oxide is shown in FIG. 29. Thequantum structure, generally referenced 1920, comprises two wells 1921,1927 with fin structures 1923, 1926 to realize the quantum dots #1 and#2, a gate layer with oxide 1924 overlaps both fins and creates atunneling path from one fin to the other. A diagram illustrating a threedimensional view of an example 3D semiconductor quantum structure usingfin-to-gate and gate-to-fin tunneling through oxide is shown in FIG. 30.The quantum structure, generally referenced 1930, comprises fins 1932,1938, overlapping control gate with oxide layer 1936, substrate 1931,and local depletion region 1934. Note that the well may be omitted andthe qdot realized by the semiconductor fin area only.

With reference to FIGS. 29 and 30, the tunneling is controlled by thecontrol terminal that imposes the potential on the tunneling gate. Inone embodiment, the control gate is substantially floating but it iselectrostatically coupled to the control terminal nearby (not shown). Ifthe tunnel barrier is high, the quantum particle is locked in its priorstate. When the control terminal determines a lowering of the barrier,the quantum particle is allowed to tunnel from one qdot to the other.Depending on the pulse width of the control signal, the quantum particleeither completely or partially tunnels through. In the latter case, thequantum particle is distributed between two qdots to achieve a spatialsuperposition state. A thin oxide layer separates the semiconductor finfrom the control gate. Note that in real implementations, the quantumstructure generally has a deformed complex 3D shape where the depletionregion depends on the particular implementation and semiconductorprocess used. The structures shown herein are for illustration purposesonly.

A diagram illustrating a cross section, side view, and top view of anexample 3D semiconductor quantum structure using fin-to-gate tunnelingthrough oxide is shown in FIG. 31. The quantum structure, generallyreferenced 1950, comprises substrate 1951, optional oxide layer 1957,wells 1952, fins 1953, 1955, gate oxide 1956, and overlapping controlgate 1954. Note that the dotted line indicates the optional oxide layerthat isolates the 3D quantum structure from the substrate, i.e. SOIprocess. The substrate may comprise standard resistivity, highresistivity, or isolating substrates.

The tunneling through the oxide in the quantum structure is induced in afin by the overlapping control gate. When the barrier is high, virtuallyno tunneling current is allowed. When the barrier is lowered, tunnelingthrough the gate oxide allows the particle to move from one qdot to theother. If the particle has not completed the move from one qdot to theother, it will spread (equally or non-equally) between two qdots toachieve a superposition state.

A diagram illustrating a cross section of an example 3D semiconductorquantum structure using fin-to-gate and gate-to-fin tunneling is shownin FIG. 32. The quantum structure, generally referenced 1940, comprisessubstrate 1941, optional oxide layer 1942, fins 1945, 1946, gate oxide1944, and overlapping control gate 1943. As described supra, thetunneling through the oxide layer 1944 is controlled by the overlappingcontrol terminal that imposes the potential on the control gate. If thetunnel barrier is high, the quantum particle is locked in its priorstate. When the control terminal determines a lowering of the barrier,the quantum particle is allowed to tunnel from one qdot to the other.

A diagram illustrating a top view of an example two qdot 3Dsemiconductor quantum structure using fin-to-gate tunneling throughoxide is shown in FIG. 33. The quantum structure, generally referenced1990, comprises two wells 1992, 1996 with fin structures 1993 thatrealize quantum dots #1 and #2 and a control gate layer with oxide 1994overlapping both fins creating a tunneling path 1995 for particle 1992from one fin to the other.

Note that different shapes can be used for the layers used to constructthe quantum structure, e.g., squares, rectangles, polygons, circles,composed shapes, etc. as described supra. In this embodiment, two wellsare added, one to each fin which crosses the well in the middle. Whenthe control terminal lowers the barrier, the quantum particle in theleft qdot tunnels to the right qdot.

A diagram illustrating an example double V quantum interaction structureusing 3D semiconductor process with fin-to-gate tunneling is shown inFIG. 34A. The quantum interaction gate, generally referenced 1960,comprises two 3D structures comprising a plurality of qdots 1964, fins1968, control gates 1966, and interaction qdots 1962.

In this embodiment, the inner two semiconductor wells 1962 come in veryclose proximity thereby allowing a strong interaction between particlesor distributed particles in the two qdots. The distance between otherpairs of qdots is significantly larger and thus the interaction betweencorresponding particles is much smaller, ideally negligible. In thismanner, the double V quantum structure shifts two or more particles intospecific positions for a well controlled interaction and them transportsthem apart. The preparation of the quantum state also happens whenparticles are further away and thus can be done largely independent onefrom the other. This also allows a well controlled interaction betweenparticles only when they are in specific qdots and when the controlsignals are configured to enable the interaction.

A diagram illustrating an example quantum structure with fin-to-gatetunneling with dummy gates and cuts to create dummy fins is shown inFIG. 34B. The quantum structure, generally referenced 1970, comprises aplurality of qdots 1972, fins 1973, control gates 1974, contacts 1975,dummy gates 1971 not used in operation of the circuit, and gate cuts1976. Depending on the actual 3D semiconductor process used, dummy gatesmay be needed which remain floating with no potential. The gates need tobe equally spaced and on the edges of the well. In addition, they mayneed to be cut in order to prevent unwanted interactions. The cuttingmay be done on top of a dummy fin, or alternatively without the fin.

A diagram illustrating an example hybrid planar and 3D semiconductorquantum structure using both fin-to-gate and well-to-gate tunneling isshown in FIG. 34C. The quantum structure, generally referenced 1980,comprises 3D qdots 1982, fins 1984, 1986, 3D control gate 1986, planarqdots 1988, and planar control gate 1989. This hybrid embodiment usesboth 3D and planar tunneling structures which is possible in a 3Dsemiconductor process. The inner quantum structure is planar with twowells (i.e. qdots) and uses well-to-gate tunneling through oxide. Theouter, i.e. left and right, quantum structures are 3D and use fin-to-fintunneling through oxide. Note that the two types of tunneling havedifferent barrier levels and thus require different control gatesignals.

Those skilled in the art will recognize that the boundaries betweenlogic and circuit blocks are merely illustrative and that alternativeembodiments may merge logic blocks or circuit elements or impose analternate decomposition of functionality upon various logic blocks orcircuit elements. Thus, it is to be understood that the architecturesdepicted herein are merely exemplary, and that in fact many otherarchitectures may be implemented which achieve the same functionality.

Any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality may be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediary components. Likewise, any two componentsso associated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations merely illustrative. The multipleoperations may be combined into a single operation, a single operationmay be distributed in additional operations and operations may beexecuted at least partially overlapping in time. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The use of introductory phrases suchas “at least one” and “one or more” in the claims should not beconstrued to imply that the introduction of another claim element by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim element to inventions containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles. Unless statedotherwise, terms such as “first,” “second,” etc. are used to arbitrarilydistinguish between the elements such terms describe. Thus, these termsare not necessarily intended to indicate temporal or otherprioritization of such elements. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. As numerousmodifications and changes will readily occur to those skilled in theart, it is intended that the invention not be limited to the limitednumber of embodiments described herein. Accordingly, it will beappreciated that all suitable variations, modifications and equivalentsmay be resorted to, falling within the spirit and scope of the presentinvention. The embodiments were chosen and described in order to bestexplain the principles of the invention and the practical application,and to enable others of ordinary skill in the art to understand theinvention for various embodiments with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. An interface device for interfacing betweenclassic field effect transistor (FET) circuitry and quantum circuitry,comprising: a substrate; a substantially undoped layer constructed onsaid substrate in which a quantum dot is realized; a doped source/drainregion formed over a first portion of said substantially undoped layerconstituting a classic side of said interface device connected to one ormore classic FET devices fabricated on said substrate; a control gateconstructed over at least a portion of said substantially undoped layerwherein a second portion thereof on a second side of said control gateconstitutes a quantum side of said interface device connected to one ormore quantum circuits fabricated on said substrate; and a controlcircuit operative to generate and apply an appropriate potential to saidcontrol gate to control a tunneling path thereunder thereby causing oneor more particles to tunnel between said classic side and said quantumside of said interface device.
 2. The interface device according toclaim 1, wherein the potential applied to said control gate affectstransport of said one or more particles from said classic side to saidquantum side.
 3. The interface device according to claim 1, wherein thepotential applied to said control gate effects transport of said one ormore particles from said quantum side to said classic side.
 4. Theinterface device according to claim 1, wherein a potential of saidclassic well is set to a given reference value through a reset processand the potential of said control gate is modified with respect to thereference value to establish transport of said one or more particlesfrom said classic side to said quantum side.
 5. The interface deviceaccording to claim 1, wherein said interface device is located at one orboth ends of said substantially undoped layer.
 6. The interface deviceaccording to claim 1, wherein said substrate is selected from a groupconsisting of a semiconductor, silicon on insulator (SOI), insulatingsubstrate replacement, and a bulk substrate having a global depletionlayer that isolates top devices from said substrate.
 7. The interfacedevice according to claim 1, wherein said doped source/drain region isselected from a group consisting of low doped (n−, p−), medium doped (n,p), high doped (n+, p+), and highly doped (n++, p++) and said secondwell substantially undoped layer is selected from a group consisting ofintrinsic undoped, and very low doped (n−−, p−−).
 8. The interfacedevice according to claim 1, wherein said doped source/drain region andsaid substantially undoped layer have a shape selected from a groupconsisting of: a circle, an ellipse, a square, a rectangle, a trapezoid,two squares diagonally connected at their corners, two rectanglesdiagonally connected at their corners, two squares overlapping at theircorners, two rectangles overlapping at their corners, two squaresconnected at their corners to a third smaller square, two squaresconnected at their corners to a smaller double square, two rectanglesconnected at their corners to a third smaller square, two rectanglesconnected at their corners to a smaller double square, two diagonallyoverlapping squares connected at a corner to another two diagonallyoverlapping squares, two diagonally overlapping rectangles connected ata corner to another two diagonally overlapping rectangles, a path at aninclined angle from the orthogonal axis, a path at 45 degrees from oneof the orthogonal axis, and any combination thereof.
 9. The interfacedevice according to claim 1, wherein said doped source/drain region isaligned with an edge of said control gate.
 10. The interface deviceaccording to claim 1, wherein said quantum side extends beyond an edgeof said control gate on the classic side and the doped source/drainregion is at a certain distance from the edge of said control gate. 11.The interface device according to claim 1, wherein said control gate isselected from a group consisting of a contacted control gate directlydriven by an electronic signal, metal gate or well imposed floatingcontrol gate utilizing adjacent or overlapping positioning, and afloating control gate with an imposing adjacent gate potential.
 12. Theinterface device according to claim 1, wherein said quantum side issurrounded by oxide, one or more insulating layers, and/or one or morewide depletion regions.
 13. The interface device according to claim 1,wherein the potential applied to said control gate comprises one or morepulses signal having two or more controlled amplitude levels, controlledtime duration, and controlled transition times.
 14. The interface deviceaccording to claim 1, wherein an appropriate potential applied to saidcontrol gate enables a single quantum particle to tunnel from saidclassic side to said quantum side of said device in an injector mode ofoperation.
 15. The interface device according to claim 1, wherein asingle quantum particle is transported from said quantum side to saidclassic side where its presence is detected by a detector circuitcoupled to said classic side.
 16. An interface device for interfacingbetween classic field effect transistor (FET) circuitry and quantumcircuitry, comprising: a substrate; a first well having a dopedsource/drain region constructed on said substrate in accordance with aclassic FET device to form a classic side of said interface device; acontact layer operative to establish an electric connection between ametal layer connected to one or more classic FET devices and said firstwell, said one or more FET devices fabricated on said substrate; asecond well constructed on said substrate and substantially undoped inaccordance with a quantum structure to form a quantum side of saidinterface device, said quantum side connected to one or more quantumdevices fabricated on said substrate; a control gate fabricated tooverlap at least a portion of said second well and to separate saidclassic side of said interface device from side quantum side; andwherein application of an appropriate potential to said control gateenables tunneling of one or more quantum particles through a localdepleted tunneling path formed between said classic side and saidquantum side.
 17. The interface device according to claim 16, whereinthe tunneling of a single quantum particle has the direction from saidclassic side to said quantum side of said interface device in aninjection mode of operation.
 18. The interface device according to claim16, wherein the tunneling of a single quantum particle has the directionfrom said quantum side to said classic side of said interface device ina detection mode of operation.
 19. The interface device according toclaim 16, wherein said substrate is selected from a group consisting ofa semiconductor, silicon on insulator (SOI), insulating substratereplacement, and a bulk substrate having a global depletion layer thatisolates top devices from said substrate.
 20. The interface deviceaccording to claim 16, wherein said first well is selected from a groupconsisting of low doped (n−, p−), medium doped (n, p), high doped (n+,p+), and highly doped (n++, p++), and said second well is selected froma group consisting of intrinsic undoped, and very low doped (n−−, p−−).21. The interface device according to claim 16, wherein said first andsecond well is at least one of orthogonal with said control gate, and ata specific angle from said control gate.
 22. The interface deviceaccording to claim 16, wherein the potential applied to said controlgate comprises one or more pulses having at least two controlledamplitude levels, controlled time duration, and controlled transitiontimes.
 23. An interface device for interfacing between classic fieldeffect transistor (FET) circuitry and quantum circuitry, comprising: asubstrate; a classic FET well having a doped source/drain regionconstructed on said substrate to form a classic side of said interfacedevice and operative to be connected to classic FET circuitry fabricatedon said substrate; a quantum dot well constructed on said substrate toform a quantum side of said interface device and operative to interfacewith quantum circuitry fabricated on said substrate; a control gateconstructed over at least a portion of said quantum dot well wherebysaid classic side is on a first side of said control gate and saidquantum side is on a second side thereof; wherein a first pulse signalat a first time instance applied to said control gate controls tunnelingof first one or more quantum particles through a local depleted tunnelpath from said classic side to said quantum side in an injector mode ofoperation; and wherein a second pulse signal at a second time instanceapplied to said control gate allows tunneling of second one or morequantum particles through a local depleted tunneling path from the saidquantum side to said classic side in a detector mode of operation. 24.The interface device according to claim 23, wherein said classic FETwell is selected from a group consisting of low doped (n−, p−), mediumdoped (n, p), high doped (n+, p+), and highly doped (n++, p++) and saidquantum dot well is selected from a group consisting of intrinsicundoped, and very low doped (n−−, p−−).
 25. The interface deviceaccording to claim 23, wherein said first pulse signal and said secondpulse signal applied to said control gate each comprise one or moresignals having at least two controlled amplitude levels, controlled timeduration, and transition time.
 26. The interface device according toclaim 23, wherein a third pulse signal is applied to said classic wellin the injector mode of operation.
 27. The interface device according toclaim 23, wherein said classic well is set electrically floating toenable said single quantum particle to be detected.